Move widgets from core to native and web

Also made fields private and improved `Renderer` traits.

web/src/widget/button.rs

@@ -1,11 +1,103 @@
-use crate::{Bus, Element, Widget};
+use crate::{Background, Bus, Element, Length, Widget};
 
 use dodrio::bumpalo;
 
-pub use iced_core::button::State;
+/// A generic widget that produces a message when clicked.
+pub struct Button<'a, Message> {
+    content: Element<'a, Message>,
+    on_press: Option<Message>,
+    width: Length,
+    min_width: u32,
+    padding: u16,
+    background: Option<Background>,
+    border_radius: u16,
+}
 
-pub type Button<'a, Message> =
-    iced_core::Button<'a, Message, Element<'a, Message>>;
+impl<'a, Message> Button<'a, Message> {
+    /// Creates a new [`Button`] with some local [`State`] and the given
+    /// content.
+    ///
+    /// [`Button`]: struct.Button.html
+    /// [`State`]: struct.State.html
+    pub fn new<E>(_state: &'a mut State, content: E) -> Self
+    where
+        E: Into<Element<'a, Message>>,
+    {
+        Button {
+            content: content.into(),
+            on_press: None,
+            width: Length::Shrink,
+            min_width: 0,
+            padding: 0,
+            background: None,
+            border_radius: 0,
+        }
+    }
+
+    /// Sets the width of the [`Button`].
+    ///
+    /// [`Button`]: struct.Button.html
+    pub fn width(mut self, width: Length) -> Self {
+        self.width = width;
+        self
+    }
+
+    /// Sets the minimum width of the [`Button`].
+    ///
+    /// [`Button`]: struct.Button.html
+    pub fn min_width(mut self, min_width: u32) -> Self {
+        self.min_width = min_width;
+        self
+    }
+
+    /// Sets the padding of the [`Button`].
+    ///
+    /// [`Button`]: struct.Button.html
+    pub fn padding(mut self, padding: u16) -> Self {
+        self.padding = padding;
+        self
+    }
+
+    /// Sets the [`Background`] of the [`Button`].
+    ///
+    /// [`Button`]: struct.Button.html
+    /// [`Background`]: ../../struct.Background.html
+    pub fn background(mut self, background: Background) -> Self {
+        self.background = Some(background);
+        self
+    }
+
+    /// Sets the border radius of the [`Button`].
+    ///
+    /// [`Button`]: struct.Button.html
+    pub fn border_radius(mut self, border_radius: u16) -> Self {
+        self.border_radius = border_radius;
+        self
+    }
+
+    /// Sets the message that will be produced when the [`Button`] is pressed.
+    ///
+    /// [`Button`]: struct.Button.html
+    pub fn on_press(mut self, msg: Message) -> Self {
+        self.on_press = Some(msg);
+        self
+    }
+}
+
+/// The local state of a [`Button`].
+///
+/// [`Button`]: struct.Button.html
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub struct State;
+
+impl State {
+    /// Creates a new [`State`].
+    ///
+    /// [`State`]: struct.State.html
+    pub fn new() -> State {
+        State::default()
+    }
+}
 
 impl<'a, Message> Widget<Message> for Button<'a, Message>
 where