ui: migrate `GtkDialog` to `AdwDialog`

[zefr0x]

Closes: #1120 Related: #1110

• In the UI i used ~GtkBox~ AdwToolbarView and AdwHeaderBar to replace the actions functionality that was in GtkDialog. (its a minor change, but Github's diff algorithm doesn't handle .xml files properly because of the change in the indentation)

• Rather than hiding the dialog when the file selection window is opened, the sensitive property of the dialog will be switched to false. It will be returned to true when the file selection window is closed.

• The import related dialogs are more complicated since we need to return a value.

For now just file-selection, print, and keyboard-shortcut dialogs opens in a separate window. I think we don't have a choice for the first two, but the last one is possible (if there was AdwShortcutsDialog).

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P.S. I'm not confident with my async skills so I might've done some thing wrong :)

[oscfdezdz]

In the UI i used GtkBox and AdwHeaderBar to replace the actions functionality that was in GtkDialog.

I would suggest using AdwToolbarView instead of GtkBox which is a more specific widget for this type of use because of the properties and styles it has.