Make Command implementations platform-specific

This allows us to introduce a platform-specific `Action` to both `iced_native`
and `iced_web` and remove the `Clipboard` from `Application::update` to maintain
purity.

Additionally, this should let us implement further actions to let users query
and modify the shell environment (e.g. window, clipboard, and more!)

examples/clock/src/main.rs

@@ -1,7 +1,7 @@
 use iced::{
     canvas::{self, Cache, Canvas, Cursor, Geometry, LineCap, Path, Stroke},
-    executor, time, Application, Clipboard, Color, Command, Container, Element,
-    Length, Point, Rectangle, Settings, Subscription, Vector,
+    executor, time, Application, Color, Command, Container, Element, Length,
+    Point, Rectangle, Settings, Subscription, Vector,
 };
 
 pub fn main() -> iced::Result {
@@ -40,11 +40,7 @@ impl Application for Clock {
         String::from("Clock - Iced")
     }
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::Tick(local_time) => {
                 let now = local_time;

examples/download_progress/src/main.rs

@@ -1,6 +1,6 @@
 use iced::{
-    button, executor, Align, Application, Button, Clipboard, Column, Command,
-    Container, Element, Length, ProgressBar, Settings, Subscription, Text,
+    button, executor, Align, Application, Button, Column, Command, Container,
+    Element, Length, ProgressBar, Settings, Subscription, Text,
 };
 
 mod download;
@@ -43,11 +43,7 @@ impl Application for Example {
         String::from("Download progress - Iced")
     }
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::Add => {
                 self.last_id = self.last_id + 1;

examples/events/src/main.rs

@@ -1,7 +1,7 @@
 use iced::{
-    button, executor, Align, Application, Button, Checkbox, Clipboard, Column,
-    Command, Container, Element, HorizontalAlignment, Length, Settings,
-    Subscription, Text,
+    button, executor, Align, Application, Button, Checkbox, Column, Command,
+    Container, Element, HorizontalAlignment, Length, Settings, Subscription,
+    Text,
 };
 use iced_native::{window, Event};
 
@@ -40,11 +40,7 @@ impl Application for Events {
         String::from("Events - Iced")
     }
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::EventOccurred(event) if self.enabled => {
                 self.last.push(event);

examples/game_of_life/src/main.rs

@@ -12,8 +12,8 @@ use iced::slider::{self, Slider};
 use iced::time;
 use iced::window;
 use iced::{
-    Align, Application, Checkbox, Clipboard, Column, Command, Container,
-    Element, Length, Row, Settings, Subscription, Text,
+    Align, Application, Checkbox, Column, Command, Container, Element, Length,
+    Row, Settings, Subscription, Text,
 };
 use preset::Preset;
 use std::time::{Duration, Instant};
@@ -71,11 +71,7 @@ impl Application for GameOfLife {
         String::from("Game of Life - Iced")
     }
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::Grid(message, version) => {
                 if version == self.version {

examples/integration_opengl/src/controls.rs

@@ -1,7 +1,7 @@
 use iced_glow::Renderer;
 use iced_glutin::{
-    slider, Align, Clipboard, Color, Column, Command, Element, Length, Program,
-    Row, Slider, Text,
+    slider, Align, Color, Column, Command, Element, Length, Program, Row,
+    Slider, Text,
 };
 
 pub struct Controls {
@@ -30,13 +30,8 @@ impl Controls {
 impl Program for Controls {
     type Renderer = Renderer;
     type Message = Message;
-    type Clipboard = Clipboard;
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::BackgroundColorChanged(color) => {
                 self.background_color = color;

examples/integration_wgpu/src/controls.rs

@@ -1,7 +1,7 @@
 use iced_wgpu::Renderer;
 use iced_winit::{
-    slider, Align, Clipboard, Color, Column, Command, Element, Length, Program,
-    Row, Slider, Text,
+    slider, Align, Color, Column, Command, Element, Length, Program, Row,
+    Slider, Text,
 };
 
 pub struct Controls {
@@ -30,13 +30,8 @@ impl Controls {
 impl Program for Controls {
     type Renderer = Renderer;
     type Message = Message;
-    type Clipboard = Clipboard;
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::BackgroundColorChanged(color) => {
                 self.background_color = color;

examples/menu/src/main.rs

@@ -1,7 +1,6 @@
 use iced::menu::{self, Menu};
 use iced::{
-    executor, Application, Clipboard, Command, Container, Element, Length,
-    Settings, Text,
+    executor, Application, Command, Container, Element, Length, Settings, Text,
 };
 use iced_native::keyboard::{Hotkey, KeyCode, Modifiers};
 
@@ -92,11 +91,7 @@ impl Application for App {
         ])
     }
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::MenuActivated(entry) => self.selected = Some(entry),
         }

examples/pane_grid/src/main.rs

@@ -1,8 +1,7 @@
 use iced::{
     button, executor, keyboard, pane_grid, scrollable, Align, Application,
-    Button, Clipboard, Color, Column, Command, Container, Element,
-    HorizontalAlignment, Length, PaneGrid, Row, Scrollable, Settings,
-    Subscription, Text,
+    Button, Color, Column, Command, Container, Element, HorizontalAlignment,
+    Length, PaneGrid, Row, Scrollable, Settings, Subscription, Text,
 };
 use iced_native::{event, subscription, Event};
 
@@ -51,11 +50,7 @@ impl Application for Example {
         String::from("Pane grid - Iced")
     }
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::Split(axis, pane) => {
                 let result = self.panes.split(

examples/pokedex/src/main.rs

@@ -1,6 +1,6 @@
 use iced::{
-    button, futures, image, Align, Application, Button, Clipboard, Column,
-    Command, Container, Element, Length, Row, Settings, Text,
+    button, futures, image, Align, Application, Button, Column, Command,
+    Container, Element, Length, Row, Settings, Text,
 };
 
 pub fn main() -> iced::Result {
@@ -48,11 +48,7 @@ impl Application for Pokedex {
         format!("{} - Pokédex", subtitle)
     }
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::PokemonFound(Ok(pokemon)) => {
                 *self = Pokedex::Loaded {

examples/solar_system/src/main.rs

@@ -8,8 +8,8 @@
 //! [1]: https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API/Tutorial/Basic_animations#An_animated_solar_system
 use iced::{
     canvas::{self, Cursor, Path, Stroke},
-    executor, time, window, Application, Canvas, Clipboard, Color, Command,
-    Element, Length, Point, Rectangle, Settings, Size, Subscription, Vector,
+    executor, time, window, Application, Canvas, Color, Command, Element,
+    Length, Point, Rectangle, Settings, Size, Subscription, Vector,
 };
 
 use std::time::Instant;
@@ -48,11 +48,7 @@ impl Application for SolarSystem {
         String::from("Solar system - Iced")
     }
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::Tick(instant) => {
                 self.state.update(instant);

examples/stopwatch/src/main.rs

@@ -1,6 +1,6 @@
 use iced::{
-    button, executor, time, Align, Application, Button, Clipboard, Column,
-    Command, Container, Element, HorizontalAlignment, Length, Row, Settings,
+    button, executor, time, Align, Application, Button, Column, Command,
+    Container, Element, HorizontalAlignment, Length, Row, Settings,
     Subscription, Text,
 };
 use std::time::{Duration, Instant};
@@ -49,11 +49,7 @@ impl Application for Stopwatch {
         String::from("Stopwatch - Iced")
     }
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::Toggle => match self.state {
                 State::Idle => {

examples/todos/src/main.rs

@@ -1,7 +1,7 @@
 use iced::{
     button, scrollable, text_input, Align, Application, Button, Checkbox,
-    Clipboard, Column, Command, Container, Element, Font, HorizontalAlignment,
-    Length, Row, Scrollable, Settings, Text, TextInput,
+    Column, Command, Container, Element, Font, HorizontalAlignment, Length,
+    Row, Scrollable, Settings, Text, TextInput,
 };
 use serde::{Deserialize, Serialize};
 
@@ -58,11 +58,7 @@ impl Application for Todos {
         format!("Todos{} - Iced", if dirty { "*" } else { "" })
     }
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match self {
             Todos::Loading => {
                 match message {

examples/url_handler/src/main.rs

@@ -1,6 +1,6 @@
 use iced::{
-    executor, Application, Clipboard, Command, Container, Element, Length,
-    Settings, Subscription, Text,
+    executor, Application, Command, Container, Element, Length, Settings,
+    Subscription, Text,
 };
 use iced_native::{
     event::{MacOS, PlatformSpecific},
@@ -34,11 +34,7 @@ impl Application for App {
         String::from("Url - Iced")
     }
 
-    fn update(
-        &mut self,
-        message: Message,
-        _clipboard: &mut Clipboard,
-    ) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Command<Message> {
         match message {
             Message::EventOccurred(event) => {
                 if let Event::PlatformSpecific(PlatformSpecific::MacOS(