Implement support for output power management

This patch is based on the original stale patch by Guido Cella @guidocella.
It has been modified to apply cleanly to the latest v5.0 tag. Since the SLOC
limit is now lifted, this core feature should be merged into dwl upstream.

Thanks to Dima Krasner @dimkr for the cherry-pick.

Closes: #559, #525

Merge remote-tracking branch 'upstream/main' into wlroots-next

delete the idle protocol xml file

update layer-shell protocol to version 4

Tracking with breaking change from swaywm/wlroots@b7dc4f2.

Merge updates from guidocella

Thanks so much for helping to keep the project running while life was
crazy!

Merge pull request #49 from guidocella/layer-shell

Layer shell

Implement the idle protocol

It allows clients such as swayidle and chat applications to monitor user
idle time.

layer shell initial attempt