Pretty direct and straightforward port. This requires a GNOME Shell counterpart. In addition to that, include a progress function. https://gitlab.gnome.org/GNOME/mutter/merge_requests/458
And add the necessary glue so those initialize a X11 clutter backend. This should get Clutter tests that are dependent on windowing to work again, thus they were enabled back again. https://gitlab.gnome.org/GNOME/mutter/merge_requests/672
Clutter doesn't hold anymore backend implementations, move tests where we have one that we may assign. https://gitlab.gnome.org/GNOME/mutter/merge_requests/672
