This class sits between ClutterInputDevice and the backend implementations,
it will be the despositary of features we need across both backends, but
don't need to offer through Clutter's API.
As a first thing to have there, add a getter for a WacomDevice. This is
something scattered across and somewhat inconsistent (eg. different places
of the code create wacom devices for different device types). Just make it
here for all devices, so users can pick.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1109
The end goal is to have all clutter backend code in src/backends. Input
is the larger chunk of it, which is now part of our specific
MutterClutterBackendX11, this extends to device manager, input devices,
tools and keymap.
This was supposed to be nice and incremental, but there's no sane way
to cut this through. As a result of the refactor, a number of private
Clutter functions are now exported for external backends to be possible.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/672
