[Java][FlightRPC] FlightData deserializer should accept missing fields #26885

To be compatible with Protobuf implementations, missing fields should not be treated as an error. The C++ implementation has the same issue, and this is causing issues with the C# and Rust implementations (and presumably the Go implementation)

Reporter: David Li / @lidavidm
Assignee: David Li / @lidavidm

Related issues:

• [C#][FlightRPC] incompatible with java client for empty record batches (relates to)
• [C++][FlightRPC] Missing protobuf data_body should result in default value of empty bytes, not null (relates to)

PRs and other links:

• GitHub Pull Request #8963

_{Note: This issue was originally created as ARROW-10962. Please see the migration documentation for further details.}