feat(workspaces): style based upon workspace having windows

[antlilja]

Adds the ability to style workspaces based upon it containing any windows using the empty css class.

Example:

.workspaces .item:not(.empty) label {
    font-weight: bold;
}

I've only implemented this for hyprland so far. I wanted to open up this draft PR to see if this is a desired feature before continuing on implementing it for sway and niri.

[JakeStanger]

I'm happy for this to be added, but some consideration is needed as to how this will work with #820.

I also think this would be better inverted btw, ie an .empty class. Not empty becomes the default of omitted, and you can use :not(.empty) where required that way, which avoids the double negative.

[antlilja]

Totally agree with empty over notempty, much cleaner. I've pushed a change to switch to the empty css class instead.

I took a look at ext-workspace-v1 as well as the IPC for sway and niri. It does not seem to be possible to implement this feature for the wayland extension. Both Niri and Sway seem possible to implement this feature in.

[JakeStanger]

Yeah I suspect the play will be having an (optional) IPC layer on top of the wayland layer to bring in the extra functionality. I don't think it'll have too much impact at this stage, but worth keeping in mind.