FileConflictDialog: Gtk4 prep

[danirabbit]

Includes changes from #2225

• Remove skip_taskbar_hint
• Boxes instead of Grids
• Use child property where appropriate

[jeremypw]

Would it be better to target this at make-compile otherwise it creates conflicts that need resolving and make it compile under Gtk4?

[danirabbit]

@jeremypw ideally I’d like to reduce the size of #2225 which is why I’m targeting main. There’s a lot we could do so that we’re reviewing much smaller branches at a time and hopefully avoiding a lot of regressions. And then it’ll be a lot more feasible to actually review #2225 when the changes are smaller

[jeremypw]

But this creates extra work keeping #2225 non-conflicting.

I cannot see a way of switching from Gtk3 to Gtk4 in one buildable commit while building all the UI without it being large.

If you want to work on main under Gtk3 then we had better close #2225 and start again once work on main is done.

[danirabbit]

@jeremypw I think having a PR like #2225 is good to be able to see where we're needing to make changes, but there is a really a lot of things we could do to avoid regression and make the port much much smaller. Even if that's like a 3,000 line diff versus a 6,000 line diff I think in the long run this would save us a lot of time trying to hunt down bugs and regressions that could be avoided