Port to Gtk4

[treppenwitz03]

Goes with https://github.com/elementary/switchboard/pull/231

Blocked by:

• [x] Depends on https://github.com/elementary/switchboard/pull/231

Todo:

• [x] Test on device with battery

[lenemter]

I had to change the way authentication works. Here permission is asked on opening combobox. Trying to replicate the way auth in master works gives this:

[jeremypw]

There are some visual glitches at the moment when using gtk4 which may not be to do with code you have written. Either from upstream or maybe Gala. It would be better to maintain the behaviour approved for Gtk3 if at all possible. I'll have a look into it.

[jeremypw]

CI failing because of upstream issue. See https://github.com/elementary/docker/issues/25

[lenemter]

@jeremypw Yes, it does. But I found a big issue in both gtk3 and gtk4 versions. While authentication dialog is open, focus settings window using alt+tab or click and wait, after a short time "Not responding" window starts pop up every 5 seconds, even after you close auth dialog and power plug itself

[lenemter]

I found the exact same issue in gtk3 locale plug

[jeremypw]

As the same problem occurs in more than one plug I am going to raise a separate issue.