This is useful if you have a session, and want to "hot-plug" new sources over time; there is no point in having to create separate sessions for this. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2131>
Place the XML files in data/dbus-interfaces. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2126>