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);

crates/egui_demo_app/tests/snapshots/imageviewer.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:e6cc6ff64eb73ddac89ecdacd07c2176f3ab952c0db4593fccf6d11f155ec392
-size 103100
+oid sha256:2292f0f80bfd3c80055a72eb983549ac2875d36acb333732bd0a67e51b24ae4f
+size 102983