[FlightRPC][Java] CallbackBackpressureStrategy should not rely on listener.isReady()

According to the spec for , we can get into a state where the ready flag on the listener has already switched back to false by the time we execute the on ready handler.

We currently use the listener's ready flag after the ready handler to check if we received a spurious wake, but it's not reliable because of this. Instead we should use our own readiness flag that gets set within a synchronized block local to the CallbackBackpressureStrategy.

**Reporter**: [James Duong](https://issues.apache.org/jira/browse/ARROW-15876) / @jduo

_{**Note**: *This issue was originally created as [ARROW-15876](https://issues.apache.org/jira/browse/ARROW-15876). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Comece com CallbackBackpressureStrategy e a especificação de CallStreamObserver setOnReadyHandler vinculada na issue. Rastreie como o sinalizador de prontidão do listener é verificado após o ready handler e, em seguida, verifique se a conclusão não depende mais desse sinalizador do listener e usa o estado de prontidão sincronizado da estratégia.

Escrita pelo modelo de indexação a partir do texto da issue.