addObserver(for:using:)
Declaration
func addObserver<Notice>(for noticeType: Notice.Type, using observer: @escaping (Notice) -> Void) -> USDStage.ObservationToken where Notice : USDStage.Noticefunc addObserver<Notice>(for noticeType: Notice.Type, using observer: @escaping (Notice) -> Void) -> USDStage.ObservationToken where Notice : USDStage.Notice