feat!: Add CameraComponent to FlameGame

[spydon]

Description

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

Checklist

• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.

Migration instructions

We'll treat this as a breaking change since the cameraComponent name will clash with many of our users implementations, luckily it is very easy to migrate.

If you have a game like this currently:

class MyGame extends FlameGame {
  late final CameraComponent cameraComponent;
  late final World world;

  Future<void> onLoad() async {
    world = World()
    cameraComponent = CameraComponent(world: world);
    add(world);
    add(cameraComponent);
    world.add(MyComponent());
  }
}

then you simply have to remove your own references to cameraComponent and world, so that it becomes like this:

class MyGame extends FlameGame {
  Future<void> onLoad() async {
    world.add(MyComponent());
  }
}

If you are using CameraComponent.withFixedResolution you can migrate to this:

class MyGame extends FlameGame {
  MyGame() : super(
    cameraComponent: CameraComponent.withFixedResolution(
      width: 800,
      height: 600,
    ),
  );

  Future<void> onLoad() async {
    world.add(MyComponent());
  }
}