Show similar monitor labels in both Wayland and X11 sessions

[jeremypw]

Builds on #401 but retains functionality in X11 for now.

Can anyone advise why this fails CI on stable? Maybe @leolost2605? It is caused by the use of PantheonWayland.ExtendedBehavior but this does not cause any problem when compiling locally (however I am on the "daily" iso). The dependency is found on the stable CI but I guess it is not up to date yet.

[jeremypw]

Puzzling why CI fails in stable - for some reason the ExtendedBehaviour interface is not recognized or is different there.

[jeremypw]

@danirabbit I see that the make_monitor_label method was added after the last stable release of pantheon-wayland - presumably causing the CI failure. Is there any reason why a stable release of that library cannot be made? I see you made the previous one.

[zeebok]

The code looks good to me. I can try to test it if you'd like but last time I used Classic Session is was not stable for me for whatever reason :-/

[flodavid]

“window labels” should be replaced by “monitor labels” in the PR title I think ?

[leolost2605]

I think we should try to get #401 working for everyone so that we don't get two completely different code paths. The infrastructure on the gala side should be in place for that and for me it's already working

[flodavid]

I tested this and it does fix the issue introduced by #401 on X