Documents tabs behaviour in Gtk4 apps

[grofaty]

I reported bug 2006717 that was fixed, thanks. But now I am looking more deep into how Gtk3 vs. Gtk4 applications handle tabs and I see:

GTK3 APPLICATIONS
- First document appears as first tab, which is sized to "small" size
- Second document just new tab is added.
I think we should leave Pinta 2.1.x in this way, to be compatible with existing Gtk3 applications experience.

GTK4 APPLICATIONS
Now I see Gtk4 apps by default use little bit different approach to tabs.
- If there is single document there is no tab.
- If second document is opened then two tabs appear stretched to whole screen size.
See attachment for two Gtk4 apps.
My suggestion is for Pinta/Gtk4 to adopt this behavior to use Gtk4 applications approach. I suggest to mark this "bug report" as feature request.

[Cameron White (cameronwhite91)]

This should be easy to do - in the GTK4 branch we are already using https://gnome.pages.gitlab.gnome.org/libadwaita/doc/main/class.TabBar.html so this is just a matter of configuring the expansion and autohide settings

[Cameron White (cameronwhite91)]

Fixed by https://github.com/PintaProject/Pinta/commit/4bb3678b3b3463cbfc41876dd68b3505e375c4f5