meta_window_(un)queue() was implemented with global arrays in window.c
that managed MetaLater handle IDs and lists of window queues. In order
to rely less on scattered static variables and making it clearer that
we're dealing with per display window management and not something
specific to a single window, move the window resize/calc-showing queue
management to MetaDisplay.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2264>
As with the compositor type enum, also have the X11 display policy enum,
as it's also effectively part of the context configuration. But as with
the compositor type, move it to a header file for enums only, and since
this is a private one, create a private variant meta-enums.h.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1861>