It's a functionality from the application centric clutter that we don't need for compositors. https://gitlab.gnome.org/GNOME/mutter/merge_requests/616
It cuts away a bit of the GObject boilerplate, gives us support for `g_autoptr`, and removes the typedef hack inside clutter-content.c. https://gitlab.gnome.org/GNOME/mutter/merge_requests/380