Move widgets from core to native and web

Also made fields private and improved `Renderer` traits.

native/src/renderer/null.rs

@@ -0,0 +1,143 @@
+use crate::{
+    button, checkbox, column, radio, row, scrollable, text, text_input,
+    Background, Color, Element, Font, HorizontalAlignment, Layout, Point,
+    Rectangle, Renderer, Size, VerticalAlignment,
+};
+
+pub struct Null;
+
+impl Renderer for Null {
+    type Output = ();
+}
+
+impl column::Renderer for Null {
+    fn draw<Message>(
+        &mut self,
+        _content: &[Element<'_, Message, Self>],
+        _layout: Layout<'_>,
+        _cursor_position: Point,
+    ) {
+    }
+}
+
+impl row::Renderer for Null {
+    fn draw<Message>(
+        &mut self,
+        _content: &[Element<'_, Message, Self>],
+        _layout: Layout<'_>,
+        _cursor_position: Point,
+    ) {
+    }
+}
+
+impl text::Renderer for Null {
+    fn default_size(&self) -> u16 {
+        20
+    }
+
+    fn measure(
+        &self,
+        _content: &str,
+        _size: u16,
+        _font: Font,
+        _bounds: Size,
+    ) -> (f32, f32) {
+        (0.0, 20.0)
+    }
+
+    fn draw(
+        &mut self,
+        _bounds: Rectangle,
+        _content: &str,
+        _size: u16,
+        _font: Font,
+        _color: Option<Color>,
+        _horizontal_alignment: HorizontalAlignment,
+        _vertical_alignment: VerticalAlignment,
+    ) {
+    }
+}
+
+impl scrollable::Renderer for Null {
+    fn is_mouse_over_scrollbar(
+        &self,
+        _bounds: Rectangle,
+        _content_bounds: Rectangle,
+        _cursor_position: Point,
+    ) -> bool {
+        false
+    }
+
+    fn draw(
+        &mut self,
+        _scrollable: &scrollable::State,
+        _bounds: Rectangle,
+        _content_bounds: Rectangle,
+        _is_mouse_over: bool,
+        _is_mouse_over_scrollbar: bool,
+        _offset: u32,
+        _content: Self::Output,
+    ) {
+    }
+}
+
+impl text_input::Renderer for Null {
+    fn default_size(&self) -> u16 {
+        20
+    }
+
+    fn draw(
+        &mut self,
+        _bounds: Rectangle,
+        _text_bounds: Rectangle,
+        _cursor_position: Point,
+        _size: u16,
+        _placeholder: &str,
+        _value: &text_input::Value,
+        _state: &text_input::State,
+    ) -> Self::Output {
+    }
+}
+
+impl button::Renderer for Null {
+    fn draw(
+        &mut self,
+        _bounds: Rectangle,
+        _cursor_position: Point,
+        _is_pressed: bool,
+        _background: Option<Background>,
+        _border_radius: u16,
+        _content: Self::Output,
+    ) -> Self::Output {
+    }
+}
+
+impl radio::Renderer for Null {
+    fn default_size(&self) -> u32 {
+        20
+    }
+
+    fn draw(
+        &mut self,
+        _bounds: Rectangle,
+        _is_selected: bool,
+        _is_mouse_over: bool,
+        _label: Self::Output,
+    ) {
+    }
+}
+
+impl checkbox::Renderer for Null {
+    fn default_size(&self) -> u32 {
+        20
+    }
+
+    fn draw(
+        &mut self,
+        _bounds: Rectangle,
+        _is_checked: bool,
+        _is_mouse_over: bool,
+        _label: Self::Output,
+    ) {
+    }
+}