[Java] FlightStream: how to check whether data is available in the stream in a nonblocking way;

### Describe the usage question you have. Please include as many useful details as possible.

as the title:
How to check whether data is available in the stream in a nonblocking way;

It seems that the FlightStream API only supports fetching data by calling the `next()` method in blocking; I think a nonblocking method like `tryNext()` should also be needed.

### Component(s)

Java

从 Java FlightStream API 及其阻塞式 next() 方法开始。确定在不阻塞的情况下检查数据可用性的预期契约，包括流结束时的表示方式。完成的标准是，调用方可以通过 FlightStream API 在不阻塞的情况下检查可用性。

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