Following previous commit, rename _clutter_paint_volume_init_static()
to clutter_paint_volume_init_from_actor(), and also
_clutter_paint_volume_copy_static() to
clutter_paint_volume_init_from_paint_volume().
Make clutter_paint_volume_init_from_paint_volume() follow the dst/src
semantic in its arguments, which also allows removing
_clutter_paint_volume_set_from_volume() which is exactly the same now.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4175>
3c4ec122b5