Draft: Deferred cursor move

This feature is meant to be used with VRR / Adaptive Sync. Currently cursor move drives the display at the poll rate of the mouse. This adds a deferred delay for a variety situations: To save power on battery To maintain smooth video playback (i.e. render 30fps video at 60 or 120fps) To maintain smooth gaming experience (i.e. only enforce redraw at VRR minimum Hz)

I've tried to make it as unopinionated as possible, while also reducing complexity for downstream developers.

The design should be backwards compatible, as long as wlr_set_cursor_max_latency() is never called wlr_cursor_move() should act as normal

I considered using wl_signals, but I'm not familiar with the interface, and it felt somewhat overkill.

There's a reference implementation in branch deferred-cursor-move: https://github.com/YellowOnion/sway/commit/deferred-cursor-move

I developed this against v0.16, can try rebasing once I got wayland-protocols updated.