Add protocol to toggle output dpms
Created by: agx
Since #38 doesn't deal with output DPMS it would be good to be able to toggle an output's power save mode via a wayland protocol. I have put together a prototype in phoc/phosh to see how things go:
If it makes sense I'd like to turn it into a wlr-output-dpms so phosh can continue to run with other compositors and other shell's/daemons don't need to grow custom protocol. In this case should we still call it DPMS? Modern drm mostly treats it as legacy and does on/off only. However keeping different states gives the compositor more room like e.g. only turning off the backlight on standby and fully turning off the display pipeline on off. This is something e.g. needed on a phone since the time to bring back the display pipeline from off is too long when the user expects a quick unblank.