Changes the running scene to a new instance of the given [PackedScene].
Returns [constant OK] on success or [constant ERR_CANT_CREATE] if the scene cannot be instantiated.
[b]Note:[/b] The scene change is deferred, which means that the new scene node is added on the next idle frame. You won't be able to access it immediately after the [method change_scene_to] call.
[b]Note:[/b] Passing a value of [code]null[/code] into the method will unload the current scene without loading a new one.