Get button mapping from libwacom

Summary:
Grab evdev codes from libwacom and convert them into xsetwacom button
numbers
Requires libwacom 0.29
Add a crude "test" that compares local database data with libwacom data

This should make libwacom a suitable substitute for local database,
excluding status led info and button layout picture

BUG: 316837

Test Plan:
Hard to test this without pad buttons so a code review would suffice

I've slapped together a crude "test tool" that compares data pulled from libwacom and data pulled from local installed database
Mostly it seems to match, ignoring the button order (I don't think we care about button order, since button order can be subjective when user is filling it out using tablet finder)
Where it doesn't match it probably needs to be checked individually via google or feedback from device owner
Here's the output for the test tool if anyone's curious: https://paste.kde.org/p1cfyhxrl

Reviewers: fvogt

Differential Revision: https://phabricator.kde.org/D12075