Impl AsAssetId for SceneRoot and DynamicSceneRoot

[Glory2Antares]

Objective

• Although SceneRoot and DynamicSceneRoot are simply wrappers around a Handle<Scene>, neither implement AsAssetId. Hence they do not work with the AssetChanged<A> filter.

Solution

• Implement AsAssetId for SceneRoot and DynamicSceneRoot. Asset = Scene for both.

---

Showcase

Now users can filter for SceneRoot whose underlying Scene asset has changed.

fn query_scene_roots_with_changed_scenes(query: Query<&SceneRoot, AssetChanged<SceneRoot>>) {
    for scene_root in &query {
        println!("some logic");
    }
}