Report the monitor's connector name under Wayland
gdk_screen_get_monitor_plug_name() always returned the output name of the monitor. When using XRandR, this typically is the connector name, unless you get parse the EDID yourself, which GDK doesn't do. When using Wayland under Mutter this used to be the connector name as well, until Mutter was fixed to implement the wl_output interface properly—which provides the model and vendor of the output.
Sadly, this broke all the users of
gdk_screen_get_monitor_plug_name() that read the function's documentation, and thought that the returned string would be unique and stable as long as the monitor layout did not change.
The xdg_output interface has a
name property, which is meant to provide that information, so we might as well use it to fix the deprecated API.