clutter_input_device_get_physical_size was just used for device mapping
heuristics in MetaInputMapper. It now started using the info from udev
on for both backends, so this means this clutter API is no longer
necessary.
https://gitlab.gnome.org/GNOME/mutter/issues/514
This function call only applies to tablets, and thus will error
out unless it's called with CLUTTER_TABLET_DEVICEs. This will
allow setting absolute/relative mapping on those on the fly, as
this is optional.
This will only be practical for pads (and maybe generic buttonsets in
the future?), we just need to know the number as the events will also
contain a number as the identificator.
