Wacom tool type fixes
This fixes a number of issues with Wacom tools under Xorg
the tool type was always
UNKNOWNbut can be fetched from the property, see also (mutter!250 (merged))
if the touch device was the first one to send events, all subsequent tools would use the touch device. this only happens when the wacom driver is handling the touch device (in most default installs libinput handles it)
the serial number is shared across tool types, so the tool was always whichever one was the first in proximity. Arguably the second commit isn't required because the third commit would fix the issue too. But we don't need a tool for the touch part, so we might as well leave it in.
This is currently based on 3.24 but the code hasn't changed in master and 3.24 is much easier to test here (I can't get master to compile). I'll rebase/test once I get a yay/nay.