xi: Implement support for XI 2.4 touchpad gestures
This implements support for XI 2.4 touchpad gestures described in a spec draft in this MR: xorg/proto/xorgproto!18
The MR effectively routes libinput touchpad swipe and pinch events throughout the X server.
The MR can effectively divided into three parts:
First 9 commits that perform trivial refactoring that affects the rest of X server code. It may make sense to merge these commits earlier as that would make the review of the rest of PR easier. I guess that requires an agreement that the PR is good in principle.
All other commits except p12tic/xserver@20fe52f8 implement straightforward logic.
p12tic/xserver@20fe52f8 which implements actual gesture processing logic and will need really careful review.
libinput input driver: xorg/driver/xf86-input-libinput!17
CI is broken because the MR depends on unreleased xorg-proto