Add support for wlr-layer-shell

[Hjdskes]

This protocol allows for status bars, lockscreens, virtual keyboards, et cetera.

https://github.com/swaywm/wlroots/blob/master/protocol/wlr-layer-shell-unstable-v1.xml

[dr-carlos]

Is there any progress on this issue?

[concatime]

Also, for https://git.sr.ht/~kennylevinsen/wlgreet:

Note that cage is currently not supported due to it lacking wlr-layer-shell-unstable support.

[Sunderland93]

Hello. Any news about adding layer-shell support?

[Doosty]

This would be really nice for login greeters.

[th1nhhdk]

I need this for wlgreet