Makes sure that monitor specs which may be read from EDID data do not
contain characters that are invalid in XML. Makes it possible to restore
monitor configs of monitor models with characters such as '&' in them.
To make this change not break any tests, the sample monitor configs need
to be adjusted as well. Apostrophes don't strictly have to be escaped in
XML text elements. However, we now do escape the elements in
`<monitorspec>` specifically.
Closes: <https://gitlab.gnome.org/GNOME/mutter/-/issues/1011>
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1685>
Check that configurations where monitors are disabled are properly
used. Also test that old configurations with explicitly disabled
outputs are migrated properly.
https://bugzilla.gnome.org/show_bug.cgi?id=787629
