Update the file dialog Relm4 components to use gtk::FileDialog

[chriskilding]

In GTK 4.10, gtk::FileChooserNative is deprecated in favour of using gtk::FileDialog. The Relm4 file dialog components need to be updated to use this.

[AaronErhardt]

This is a bit challenging to do for Relm4 because this would require every user of relm4-components to have GTK4.10 installed which would be a large jump for the GTK4 version requirement. And regarding the file dialog, we shouldn't use GTK anyway but rather rely on portals through the ASHPD crate. But it's definitely true that the status quo is not ideal.