feat: Adding on game resize example (#3260)

Simple example to test the `onGameResize` lifecycle method.


https://github.com/user-attachments/assets/e0a874e9-f1f8-4fc3-b9bd-11a726a22794

examples/lib/stories/system/resize_example.dart

@@ -0,0 +1,30 @@
+import 'dart:ui';
+
+import 'package:flame/components.dart';
+import 'package:flame/game.dart';
+
+class ResizingRectangle extends RectangleComponent {
+  ResizingRectangle()
+      : super(
+          paint: Paint()..color = const Color(0xFFFE4813),
+        );
+
+  @override
+  void onGameResize(Vector2 size) {
+    super.onGameResize(size);
+
+    this.size = size * .4;
+  }
+}
+
+class ResizeExampleGame extends FlameGame {
+  ResizeExampleGame() : super(children: [ResizingRectangle()]);
+
+  static const description = '''
+    This example shows how to react to the game being resized.
+
+    The rectangle will always be 40% of the screen size.
+
+    Try resizing the window and see the rectangle change its size.
+  ''';
+}