Putting together the redraw clip of the stage never really fitted nicely
with the "queue-redraw" signal emission, it forces us to emit the
signals in a batch and we also use a weird trick to get the old paint
volume that's already on-screen into the final redraw clip (we call
_clutter_actor_propagate_queue_redraw() on the stage).
So start breaking up this association by making the stage explicitely
request the redraw clip from the actor and removing the
ClutterPaintVolume argument from _clutter_actor_finish_queue_redraw().
This is done by adding a private function
clutter_actor_get_redraw_clip() which returns our old (currently
visible) paint volume and the new paint volume.
This also allows removing the check whether a full stage redraw has been
queued in clutter_actor_real_queue_redraw() and we can now just stop the
signal emission if a propagation happened at least once.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1511>
9b16eff784