Part of #121565. Updates `get_editable_frames_for_layer` and `retrieve_editable_drawings_grouped_per_frame` functions to not use drawing indices, but the `get_drawing_at` function.
Part of #121565. Updates `get_editable_frames_for_layer` and `retrieve_editable_drawings_grouped_per_frame` functions to not use drawing indices, but the `get_drawing_at` function.