Draft TextInput widget structure

Also started a `todos` example to showcase it!

native/src/widget/text_input.rs

@@ -0,0 +1,84 @@
+use crate::{
+    Element, Event, Hasher, Layout, Length, Node, Point, Rectangle, Style,
+    Widget,
+};
+
+pub use iced_core::{text_input::State, TextInput};
+
+impl<'a, Message, Renderer> Widget<Message, Renderer> for TextInput<'a, Message>
+where
+    Renderer: self::Renderer,
+    Message: Clone + std::fmt::Debug,
+{
+    fn node(&self, renderer: &Renderer) -> Node {
+        let text_bounds =
+            Node::new(Style::default().width(Length::Fill).height(
+                Length::Units(self.size.unwrap_or(renderer.default_size())),
+            ));
+
+        Node::with_children(
+            Style::default()
+                .width(self.width)
+                .max_width(self.width)
+                .padding(self.padding),
+            vec![text_bounds],
+        )
+    }
+
+    fn on_event(
+        &mut self,
+        _event: Event,
+        _layout: Layout<'_>,
+        _cursor_position: Point,
+        _messages: &mut Vec<Message>,
+        _renderer: &Renderer,
+    ) {
+    }
+
+    fn draw(
+        &self,
+        renderer: &mut Renderer,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> Renderer::Output {
+        let bounds = layout.bounds();
+        let text_bounds = layout.children().next().unwrap().bounds();
+
+        renderer.draw(&self, bounds, text_bounds, cursor_position)
+    }
+
+    fn hash_layout(&self, state: &mut Hasher) {
+        use std::any::TypeId;
+        use std::hash::Hash;
+
+        TypeId::of::<TextInput<'static, ()>>().hash(state);
+
+        self.width.hash(state);
+        self.max_width.hash(state);
+        self.padding.hash(state);
+        self.size.hash(state);
+    }
+}
+
+pub trait Renderer: crate::Renderer + Sized {
+    fn default_size(&self) -> u16;
+
+    fn draw<Message>(
+        &mut self,
+        text_input: &TextInput<'_, Message>,
+        bounds: Rectangle,
+        text_bounds: Rectangle,
+        cursor_position: Point,
+    ) -> Self::Output;
+}
+
+impl<'a, Message, Renderer> From<TextInput<'a, Message>>
+    for Element<'a, Message, Renderer>
+where
+    Renderer: 'static + self::Renderer,
+    Message: 'static + Clone + std::fmt::Debug,
+{
+    fn from(button: TextInput<'a, Message>) -> Element<'a, Message, Renderer> {
+        Element::new(button)
+    }
+}