vblankmanager: Port to timerfd

[misyltoad]

Ports vblankmanager to be timerfd based, and also fxies issues
with re-arming at higher refresh rates.

The old nudge thread method still exists (and is needed for VR), and
it has also been improved to fix the re-arming issue.

The old method can be enabled with GAMESCOPE_DISABLE_TIMERFD.

This additionally ports the main poll event loop to epoll with the new waitable system and fixes a presentWaitID bug in Vulkan.

cc: @sharkautarch Probably interests you?

[misyltoad]

Some things to think about before merging:

• Is drawTime correct and good to use like this? Given there can be other work in steamcompmgr that is now polling this where the ulWakeupTime comes from.
• Go through games and check frame pacing

[misyltoad]

Thoughts:

Because we are using timerfd, ulWakeupTime should actually be the target point of the timerfd when using that, not the the current time from OnPollIn, so we can account for the scheduling quantums from the target wakeup time and other work (like we were wrt the pipe write before)

[misyltoad]

Seems like there is some unstable frametiming introduced by:

commit 46bbf7214ca99a2df13df3de569eb6016e5eeb05
Author: Joshua Ashton <joshua@froggi.es>
Date:   Wed Dec 6 22:51:33 2023 +0000

    steamcompmgr: Move main poll event loop to new waitable system

Not sure why yet...

[misyltoad]

Fixed that, it was because nudge_steamcompmgr was not nudging the new FD on the g_SteamCompMgrWaiter but the old global nudge one that is now unused.

[sharkautarch]

cc: @sharkautarch Probably interests you?

I merged this PR into my own branch nvidia-fix-vblank-timerfd
Initial testing w/ vkcube: works well when running w/ ENABLE_GAMESCOPE_WSI=1, but stutters with ENABLE_GAMESCOPE_WSI=0

note: not sure if it would behave better w/ --rt, because gamescope nvidia-fix/nvidia-fix-vblank-timerfd freezes when run with CAP_SYS_NICE privileges due to nvidia driver snafu

EDIT: seems like the behavior is better, less stuttery w/ intel igpu (I think because of the compute queue that could be used when not running on nvidia) , and maybe slightly more better with intel igpu + running w/ realtime (--rt)

[misyltoad]

If you are testing on NVIDIA I am not surprised at there being issues without WSI given the whole xserver interaction there.