Shape refactor (#705)

* More introspection stats about vertices/indices etc

* more serde derive

* #[inline] to Shape constructors

* Introduce RectShape

* Introduce CircleShape

* Introduce PathShape

* More serde derive

* impl Copy for RectShape and CircleShape

* Simplify some code

* More serde derive

* Add helpers for appending more input or output

* Serde derives for RawInput

* Rename Fonts::from_definitions to Fonts::new

* Add Output::take

* refactor EguiGlium slightly

* Derive PartialEq for RawInput

* Improve egui::util::History interface

* tweaks

* Improve History filter: add minimum length

* Calculate galley bounding rect

* tessellator: cull line segments and paths

* tessellator: cull meshes

* Fix bug in History bandwidth estimator

egui_demo_lib/src/apps/demo/drag_and_drop.rs

@@ -65,7 +65,7 @@ pub fn drop_target<R>(
 
     ui.painter().set(
         where_to_put_background,
-        Shape::Rect {
+        epaint::RectShape {
             corner_radius: style.corner_radius,
             fill,
             stroke,