Add UnloadSceneAsync and SetActive to SceneReference

[Deadcows]

Discussed in https://github.com/Deadcows/MyBox/discussions/200

^{Originally posted by St0wy June 15, 2022}
It would be nice if the SceneReference type had UnloadSceneAsync and SetActive methods.

I was able to have this functionnality by myself using extension methods :

public static AsyncOperation UnloadSceneAsync(this SceneReference sceneReference)
{
    return SceneManager.UnloadSceneAsync(sceneReference.SceneName);
}

public static bool SetActive(this SceneReference sceneReference)
{
    return SceneManager.SetActiveScene(SceneManager.GetSceneByName(sceneReference.SceneName));
} 

But it would be nice if it was here by default.