Add AnimationSystem and Sprite3dSystem system sets

[mgi388]

The animation system updates texture_atlas.index. The sprite3d systems operate on texture_atlas.index. So I think that the sprite3d systems should run after animation.

This manifests in my project as me needing this system ordering:

• In Update, I am changing the animation of my entity.
• In PostUpdate, I am setting the Sprite3D anchor and custom_size but these values must be obtained from the current animation frame, and that requires using texture_atlas.index. This means this system needs to run after AnimationSystem. But it also needs to run before Sprite3dSystem because I am setting anchor and custom_size which Sprite3dSystem of course is looking at.

In project the use looks something like this:

app.add_systems(
    Update,
    update_animations,
    .run_if(in_state(AppState::MyState)),
);

app.add_systems(
    PostUpdate,
    update_anchor_and_size
        .after(AnimationSystem)
        .before(Sprite3dSystem)
        .run_if(in_state(AppState::MyState)),
);

[merwaaan]

Thanks 👌