As it was originally the function to be used before
making it private and providing safer wrappers around it for x11/win32.
Nowadays, it is only used in x11 and only internally in mutter, exposing
a 'safer' variant costs us exposing more of x11 renderer APIs without
much benefits.
With this change, the only internal xlib renderer we need from meta is
set_foreign_display which can't be easily worked around
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3910>
a9ec604eba