Move widgets from core to native and web

Also made fields private and improved `Renderer` traits.

wgpu/src/primitive.rs

@@ -1,4 +1,7 @@
-use iced_native::{text, Background, Color, Font, Rectangle, Vector};
+use iced_native::{
+    Background, Color, Font, HorizontalAlignment, Rectangle, Vector,
+    VerticalAlignment,
+};
 
 #[derive(Debug, Clone)]
 pub enum Primitive {
@@ -12,8 +15,8 @@ pub enum Primitive {
         color: Color,
         size: f32,
         font: Font,
-        horizontal_alignment: text::HorizontalAlignment,
-        vertical_alignment: text::VerticalAlignment,
+        horizontal_alignment: HorizontalAlignment,
+        vertical_alignment: VerticalAlignment,
     },
     Quad {
         bounds: Rectangle,