#19 "Eraser" button doesn't work with KYE tablets

[Nikolai Kondrashov]

Many KYE tablets come with the "Eraser" button, which currently doesn't work and instead does something else, like "Redo".

This is because it is reported with a separate report ID, so it is reported in an input device separate from the pen, along with the rest of frame buttons.

To properly report it, so it could be handled by xf86-input-wacom, it needs to be reported as BTN_TOOL_ERASER in the pen input device.

To do that we will probably need to create a synthetic input device and aggregate both the pen reports and the "Eraser" button reports there.