input/pointer: add functions for modifying pointer state
Created by: Xyene
These allow a compositor to do things like skip motion events on pointer constraint unlock, or not move the pointer during touch emulation.
Refs swaywm/sway#5431, swaywm/sway#5459.
Marked as draft until the Sway-side PRs are updated / we decide if this is how we want to do this.