This mapper hooks into CLUTTER_BUTTON_PRESS/RELEASE events with a
clutter button of zero but a nonzero evcode (e.g. BTN_STYLUS).
It then looks up the available button actions and implements
switch-monitor and keybindings using the MetaTabletActionMapper parent
class.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3649>
