In all places (including src/wayland) we tap into meta_x11_display* focus
API, which then calls meta_display* API. This relation is backwards, so
rework input focus management so it's the other way around.
We now have high-level meta_display_(un)set_input_focus functions, which
perform the backend-independent maintenance, and calls into the X11
functions where relevant. These functions are what callers should use.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/420