This is typically implemented as a combobox or, for boolean choices,
as a checkbutton. You can select a value using
[method@Gtk.FileChooser.set_choice] before the dialog is shown,
and you can obtain the user-selected value in the
[signal@Gtk.Dialog::response] signal handler using
[method@Gtk.FileChooser.get_choice].
Adds a 'choice' to the file chooser.
This is typically implemented as a combobox or, for boolean choices, as a checkbutton. You can select a value using [method@Gtk.FileChooser.set_choice] before the dialog is shown, and you can obtain the user-selected value in the [signal@Gtk.Dialog::response] signal handler using [method@Gtk.FileChooser.get_choice].