Move widgets from core to native and web

Also made fields private and improved `Renderer` traits.

src/native.rs

@@ -0,0 +1,51 @@
+pub use iced_winit::{
+    Align, Background, Color, Command, Font, HorizontalAlignment, Length,
+    VerticalAlignment,
+};
+
+pub mod widget {
+    pub mod button {
+        pub type Button<'a, Message> =
+            iced_winit::Button<'a, Message, iced_wgpu::Renderer>;
+
+        pub use iced_winit::button::State;
+    }
+
+    pub mod scrollable {
+        pub type Scrollable<'a, Message> =
+            iced_winit::Scrollable<'a, Message, iced_wgpu::Renderer>;
+
+        pub use iced_winit::scrollable::State;
+    }
+
+    pub mod text_input {
+        pub use iced_winit::text_input::{State, TextInput};
+    }
+
+    pub mod slider {
+        pub use iced_winit::slider::{Slider, State};
+    }
+
+    pub use iced_winit::{Checkbox, Image, Radio, Text};
+
+    #[doc(no_inline)]
+    pub use {
+        button::Button, scrollable::Scrollable, slider::Slider,
+        text_input::TextInput,
+    };
+
+    pub type Column<'a, Message> =
+        iced_winit::Column<'a, Message, iced_wgpu::Renderer>;
+
+    pub type Row<'a, Message> =
+        iced_winit::Row<'a, Message, iced_wgpu::Renderer>;
+
+    pub type Container<'a, Message> =
+        iced_winit::Container<'a, Message, iced_wgpu::Renderer>;
+}
+
+#[doc(no_inline)]
+pub use widget::*;
+
+pub type Element<'a, Message> =
+    iced_winit::Element<'a, Message, iced_wgpu::Renderer>;