Wayland daemon display labels

[leolost2605]

I had this wayland-daemon branch lying around and thought I might as well put it to use.

This removes the gala-daemon autostart and instead starts it as a wayland client on wayland or as a normal subprocess on x. It therefore also removes all the session stuff (not sure whether we have to do somewhere else something else too).

Furthermore it implements an API to show MonitorLabels which is pretty much taken from #1827 and from the original displaylabel in settings.
I've hardcoded the CSS and didn't gresource it since we need some hardcoded css anyways. If it should still be gresourced where would be the best place to put it? Normal data folder?
I'm not sure since what mutter version Meta.Context is required for WaylandClient creation so I guessed 43 which would fit with the commit date. Is there a good way to find this version?

This is an alternative to #1827 and works on both X and wayland.

Closes #1827
Fixes #1823
Probably fixes #1826

[leolost2605]

For testing one can use elementary/switchboard-plug-display#372

[bobby285271]

Given that mutter!2718 is not in 43, do you mind replacing the HAS_MUTTER43 in src/DaemonManager.vala with HAS_MUTTER44 since NixOS pins Mutter to 43 on Pantheon and we do need that to get this build 🙇

[leolost2605]

Given that mutter!2718 is not in 43, do you mind replacing the HAS_MUTTER43 in src/DaemonManager.vala with HAS_MUTTER44 since NixOS pins Mutter to 43 on Pantheon and we do need that to get this build 🙇

Sure seems I guessed wrong then 😅

[danirabbit]

@lenemter Can you take a look at this? I think these labels are currently the biggest blocker for this gtk4 port :)

[leolost2605]

I would actually kinda prefer to go with #1844 first and then I'll push a new branch with display labels based on that one since it's quite a bit better than this one and with less changes. The bigger diff there is just because I moved both menus into separate files.

[lenemter]

@leolost2605 resolve conflicts here please

[leolost2605]

See #1861