Rewrite FlightSQL client in terms of the mid level client (WIP)

[alamb]

Draft as it builds on

• Implement RecordBatch <--> FlightData encode/decode + tests #3391

Which issue does this PR close?

re #3301

closes #3310
closes #3308
closes #3400

Rationale for this change

Low level details such as encoding FlightData and specific forms of authentication should be avoided in FlightSQL as they are now present in the mid level client and so this client can be used with as many implementations as possible

What changes are included in this PR?

1. Rewrites the FlightSQL client in terms of the Flight mid level client
2. Adds a FlightSQL integration tests
3. Adds CI coverage for flight-experimental features: Add CI test coverage for flight-sql-experimental features #3400
4. TODO Move specifics of credential handling and connection management into examples client / server (e.g. handshake)

Are there any user-facing changes?

Yes; New FlightSqlClient (still behind XXXXX feature flag)

[alamb]

This has bitrotted too much -- I will redo the code if we want to pursue the idea