feat: Add displace extension to Rect (#3943)

Add displace extension to Rect.
In line with existing extensions that facilitate existing methods by
using `Vector2`.

Author: luanpotter

packages/flame/lib/src/extensions/rect.dart

@@ -80,6 +80,12 @@ extension RectExtension on Rect {
     );
   }
 
+  /// Displaces this [Rect] by the given [delta] displacement vector,
+  /// returning a new [Rect] instance. Equivalent to [shift] or [translate].
+  Rect displace(Vector2 delta) {
+    return shift(delta.toOffset());
+  }
+
   /// Generates a random point within the bounds of this [Rect].
   Vector2 randomPoint([Random? random]) {
     final randomGenerator = random ?? randomFallback;

packages/flame/test/extensions/rect_test.dart

@@ -181,6 +181,16 @@ void main() {
       expect(result.bottomRight.toVector2(), closeToVector(Vector2(20, 20)));
     });
 
+    test('test displace', () {
+      const input = Rect.fromLTWH(0, 1, 10, 10);
+      final delta = Vector2(10, 10);
+      final result = input.displace(delta);
+
+      expect(result.topLeft.toVector2(), closeToVector(Vector2(10, 11)));
+      expect(result.bottomRight.toVector2(), closeToVector(Vector2(20, 21)));
+      expect(result.size.toVector2(), closeToVector(input.size.toVector2()));
+    });
+
     testRandom('test bounding box', (Random r) {
       final points = List.generate(
         r.nextInt(15) + 2,