They're a dime a dozen. If it gets called exclusively from the
input thread, it got one. Hopefully these breadcrumbs will be
enough so people don't lose their way here.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1403>
The order and way include macros were structured was chaotic, with no
real common thread between files. Try to tidy up the mess with some
common scheme, to make things look less messy.