This makes more sense to have in the ClutterKeymap, since we have it. https://gitlab.gnome.org/GNOME/mutter/merge_requests/852
We thus far have similar objects/code internal to backends. Expose the minimum API necessary to cater for gnome-shell as a generic object. So far only the X11 backend has an actual GObject for it, and was made to be a subclass right away.