code: public static <ReqT, RespT> StreamObserver<ReqT> asyncClientStreamingCall(
        ClientCall<ReqT, RespT> call,
        StreamObserver<RespT> responseObserver) {
      return asyncStreamingRequestCall(call, responseObserver, false);
    }
docs: Executes a client-streaming call returning a {@link StreamObserver} for the request messages.
  The {@code call} should not be already started.  After calling this method, {@code call}
  should no longer be used.
  
  @return request stream observer.