Avoids using a static and make sure things are properly freed by
using g_autoptr. Also take the opportunity to add some missing NULL
initialization for auto-pointers variables
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3687>
It tests various sub-surface corner cases. It would fail without the
previous fixes.
v2:
* Fix draw_descendant parameter formatting
* Make toplevel window fullscreen (Robert Mader)
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3364>