Require a StrokeKind when painting rectangles with strokes (#5648)

This is a breaking change, requiring users to think about wether the
stroke is inside/centered/outside the rect.

When in doubt, add `egui::StrokeKind::Inside` to the function call.

crates/egui_demo_app/src/frame_history.rs

@@ -75,6 +75,7 @@ impl FrameHistory {
             style.rounding,
             ui.visuals().extreme_bg_color,
             ui.style().noninteractive().bg_stroke,
+            egui::StrokeKind::Inside,
         )));
 
         let rect = rect.shrink(4.0);