EPIC: High-level Deephaven Java API

[rcaudy]

We need to re-envision the java client API now that it must operate over grpc instead of the legacy/enterprise api.

Planned Approach:

• [Java API] Break up Table API #706: Break Up Table API into TableOperations and TableData (naming TBD)
• [Java API] WorkerConnection #707: WorkerConnection (helper class to manage connected session)
• [Java API] Explore QST Impl #710: Explore QST Design (end-to-end demo for select few operations)
• [Java API] Flush Remaining Operations for TableSpec #711: Flush implementation for all operations in the QST design. (w/buy-in on design this can be parallelized)
• [Java Client API] Viewport Improvements #712: Introduce ViewportTable API for viewport subscriptions; no longer aggregate multiple viewports over same table.

[rcaudy]

Closing this "August 2021" epic. We've delivered low and high-level Java client APIs with support for Arrow Flight (including doGet data snapshots), delta-replicated tables, synchronous table proxies, and a Query Syntax Tree (QST) implementation for batch-oriented, strongly-typed execution with fine-grained control.
The next epic will seek to address inter-worker communication, doPut support, expansion of the QST, and more.