[Flight] Make it possible to use native gRPC Java APIs, and/or simplify the implementation

### Describe the enhancement requested

https://github.com/grpc/grpc-java/pull/10318 introduces a new type of blocking stub in grpc-java which handles streaming calls. This could drastically simplify DoGet/DoPut/DoExchange which try to present blocking interfaces to nonblocking APIs. However, preferably we would make it possible to use gRPC APIs directly instead of making users wait for us to wrap new APIs in even less documented new APIs. Also, it's not clear that this simplifies the server side at all (unfortunately).

Empieza revisando grpc-java PR 10318 y las interfaces Flight DoGet, DoPut y DoExchange descritas en el issue. Compara el uso de las APIs nativas de streaming bloqueante con los wrappers actuales, incluidas las implicaciones del lado del servidor. Se considerará terminado cuando haya un enfoque claramente elegido que permita usar directamente la gRPC API o que simplifique demostrablemente la implementación.

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