feat!: Add CameraComponent to FlameGame (#2740)

This PR adds the `CameraComponent` and a `World` by default to the
FlameGame.

packages/flame_isolate/example/lib/brains/worker_overmind.dart

@@ -21,7 +21,7 @@ class WorkerOvermind extends Component
 
   @override
   Future<void> onLoad() async {
-    game.cameraComponent.viewport.add(isolateHud = WorkerOvermindHud());
+    game.camera.viewport.add(isolateHud = WorkerOvermindHud());
     super.onLoad();
   }