xwayland: Notify of root size change with XRandR emulation

Some clients (typically Java, but maybe others) rely on ConfigureNotify
or RRScreenChangeNotify events to tell that the XRandR request is
successful.

When emulated XRandR is used in Xwayland, compute the emulated root size
and send the expected ConfigureNotify and RRScreenChangeNotify events
with the emulated size of the root window to the asking X11 client.

Note that the root window size does not actually change, as XRandR
emulation is achieved by scaling the client window using viewports in
Wayland, so this event is sort of misleading.

Also, because Xwayland is using viewports, emulating XRandR does not
reconfigure the outputs location, meaning that the actual size of the
root window which encompasses all the outputs together may not change
in a multi-monitor setup. To work around this limitation, when using an
emulated mode, we report the size of that emulated mode alone as the
root size for the configure notify event.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
5 jobs for xrandr-change-notify in 10 minutes and 18 seconds (queued for 11 seconds)