The `GtkShortcutManager` interface is used to implement shortcut scopes.
This is important for [iface@Gtk.Native] widgets that have their own surface, since the event controllers that are used to implement
managed and global scopes are limited to the same native.
Examples for widgets implementing `GtkShortcutManager` are [class@Gtk.Window] and [class@Gtk.Popover].
Every widget that implements `GtkShortcutManager` will be used as a gtk_shortcut_scope_managed.