When using g_desktop_app_info_launch_uris_as_manager() the "launched"
signal allows to map a desktop-startup-id to a GAppInfo. Make this
possible for DBus activation too. Otherwise it's hard for desktop shells
to track application startup when apps are DBus activated.
It might make sense to use a different signal here since we don't have a PID and the current API says it's always set. We could also add signal detail like 'launched::dbus' vs 'launched::spawn' but my I first wanted to check if I'm on the right track.