Sequence effect with example

doc/examples/effects/sequence_effect/lib/square.dart

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+import 'package:flame/anchor.dart';
+import 'package:flame/components/component.dart';
+
+import 'dart:ui';
+
+class Square extends PositionComponent {
+  final Paint _paint;
+
+  Square(this._paint, double x, double y, {double angle = 0.0}) {
+    width = 100;
+    height = 100;
+    this.x = x;
+    this.y = y;
+    this.angle = angle;
+    anchor = Anchor.center;
+  }
+
+  @override
+  void render(Canvas canvas) {
+    prepareCanvas(canvas);
+    final rect = Rect.fromLTWH(0, 0, width, height);
+    canvas.drawRect(rect, _paint);
+  }
+}