[RFC] focus desktop when no window left

[johanmalm]

Need couple of other patches first before this can work, so haven't tested yet. Welcome thoughts on idea though.

[Consolatis]

At the current point I think this is too specific and relies on internals of desktop providing applications.

I am not quite sure how to solve this in another way though, I'd prefer some generic no-windows-available->focus-exclusive-then-ondemand-from-overlay-to-bottom instead. But that would then likely mean to randomly focus either a panel or the desktop depending on the startup order of the two (if they both use the background layer). Actually this PR will likely do the same.

Edit: There is the namespace attribute.. I think some compositors actually use that for reasons like this. The values of that string are not standardized though. https://gitlab.freedesktop.org/wlroots/wlr-protocols/-/blob/master/unstable/wlr-layer-shell-unstable-v1.xml?ref_type=heads#L67. I also don't know if wlroots even exposes it.