[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

Start with the Java FlightStream API and its blocking next() method. Determine the expected contract for checking data availability without blocking, including how the end of the stream is represented. Done means callers can check availability nonblockingly through the FlightStream API.

Written by the indexing model from the issue text.