Make headerbar match all system apps

[BAProductions]

• Switch from Gtk.HeaderBar --> Hdy.HeaderBar.
• Add close button Hdy.HeaderBar.
• Add missing headerbar.show_all ().

[lenemter]

Handy is GTK 3 library and Calculator is GTK 4 app. We now have Adwaita in GTK 4, however new header bar is not needed here. Also AFAIK we no longer need show_all in GTK 4.

[BAProductions]

[BAProductions]

Handy is GTK 3 library and Calculator is GTK 4 app. We now have Adwaita in GTK 4, however new header bar is not needed here. Also AFAIK we no longer need show_all in GTK 4.

Hold on I need to test this on my Eos 7 MV.

[TomiOhl]

Note: if the intention is to make a visually distinguishable headerbar, then it's a design conflict: Calculator was purposefully made flatter, just like some other apps (Mail, Tasks). Other system apps may follow this new direction instead in the future

[BAProductions]

eOS7 System Calculator

eOS7 System Calculator built from source

[BAProductions]

eOS7 System Calculator built from source That I get, But the app still need to respect my custom theme header bar window decoration at most.