Currently, the peripheral "output" setting will be unset if Mutter is
deciding automatically the mapped output of a tablet device. In that
case, gnome-control-center will have a hard time figuring out itself
the better output to show the tablet calibration UI, unless it's hand
held by Mutter.
Add this private D-Bus interface so that gnome-control-center can look
up the output as determined by Mutter to bring the missing harmony
between both. This interface consists of a simple method to get the
mapped output for a input device node.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2605>
