⚠️ Rename Rounding to CornerRadius (#5673)

Breaking change!

* `Rounding` -> `CornerRadius`
* `rounding` -> `corner_radius`

This is to:
* Clarify
* Conform to other systems (e.g. Figma)
* Avoid confusion with `GuiRounding`

crates/egui_demo_app/src/frame_history.rs

@@ -72,7 +72,7 @@ impl FrameHistory {
         let mut shapes = Vec::with_capacity(3 + 2 * history.len());
         shapes.push(Shape::Rect(epaint::RectShape::new(
             rect,
-            style.rounding,
+            style.corner_radius,
             ui.visuals().extreme_bg_color,
             ui.style().noninteractive().bg_stroke,
             egui::StrokeKind::Inside,

crates/egui_demo_app/src/wrap_app.rs

@@ -47,7 +47,7 @@ impl eframe::App for FractalClockApp {
             .frame(
                 egui::Frame::dark_canvas(&ctx.style())
                     .stroke(egui::Stroke::NONE)
-                    .rounding(0),
+                    .corner_radius(0),
             )
             .show(ctx, |ui| {
                 self.fractal_clock