WIP: support tablet pad keys
Some of the Wacom Cintiqs provide keyboard-like buttons
KEY_BUTTONCONFIG. They are buttons on the physical device, mapped to specific functions and labelled, see the Cintiq Pro 24. libinput currently ignores them.
This MR adds a new
LIBINPUT_EVENT_TABLET_PAD_KEY event and the associated functions. The existing
LIBINPUT_EVENT_TABLET_PAD_BUTTON isn't suitable, buttons are sequentially numbered but for these keys it matters what the keycode is.
The assumption is that the caller (e.g. mutter) either passes those on as key events to the client or launches the associated functionality directly.
Note, only the
KEY_PROG* can be routed in X, the rest is >256.
This is early work, test cases are still missing, a discussion on the high-level interface would be appreciated.