Use the provided X11 display instead of poking into GDK to get the X11 display. https://gitlab.gnome.org/GNOME/mutter/merge_requests/735
All the actual selection management functionality is superseded by MetaSelection. Reduce it to just handling the XDND messaging and leave selections to MetaSelection. https://gitlab.gnome.org/GNOME/mutter/merge_requests/320