Improve pl_queue and plplay timing loop

Drastically improves the quality and robustness of the plplay timing loop, to make it actually reflect what a "real" video player would do. Still not ideal due to the lack of vsync present feedback, but there's not much I can do on that front without the relevant timing extensions being implemented in radv/mesa.

Also includes supporting changes to pl_queue, and a new statistics dropdown on the debug menu.