From reading the comment in the top of the file, not for the first
time. Keep our own error handler and maintain our own list of
failable x11 sequences in MetaX11Display, so we can move away from
GTK's.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2864>
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.
