Add support for commit-timing-v1. no wlroots

[sergio-gdr]

Second WIP attempt at bringing support for commit-timing-v1 to gamescope. Previous attempt uses wlroots' internal infrastructure.

The protocol offers 2 target stages: presentation and latching. I've ignored the distinction for now and just take the provided timestamp to be intended for "presentation". I've also not tried to work through how a timestamp request would interact with the current implementation of fifo-v1 (something for a future iteration).