kcms/tablet: Allow assigning shortcuts to tablet touch rings

This exposes UI to rebind touch rings, like those seen on Wacom tablets. They are most similar to dials, where you can: disable them, use as a scroll wheel or bind to two arbitrary keybinds.

Needs kwin!7879 (merged), kwin!7919 (merged) and kwin!7918 (merged)

BUG: 477752 VERSION-FIXED-IN: 6.5.0

Screenshots

Current Issues

• Blocking: Need to figure out a good min/max for speed
• Current mode highlight doesn't update in realtime (tracking under https://bugs.kde.org/show_bug.cgi?id=508945)