API: Use Immutables for TableIdentifier/Namespace

[nastra]

Motivation

• Use true immutable objects that are type-safe, thread-safe, null-safe
• Get builder classes for free
• Get JSON serialization/deserialization for free (this will also be helpful for the REST-based Catalog [CORE] Specification for an HTTP REST catalog #3561)

This is relying on https://immutables.github.io/ (Apache License 2.0), which allows generating immutable objects and builders via annotation processing.

• Immutable objects are serialization ready (including JSON and its binary forms)
• Supports lazy, derived and optional attributes
• Immutable objects are constructed once, in a consistent state, and can be safely shared
  • Will fail if mandatory attributes are missing
  • Cannot be sneakily modified when passed to other code
• Immutable objects are naturally thread-safe and can therefore be safely shared among threads
  • No excessive copying
  • No excessive synchronization
• Object definitions are pleasant to write and read
  • No boilerplate setter and getters
  • No ugly IDE-generated hashCode, equals and toString methods that end up being stored in source control.

[nastra]

this is because the Immutables lib does an Objects.requireNonNull(name, "name") for everything that isn't marked as @Nullable

[nastra]

alternatively, we could add @Value.Style(throwForNullPointer = IllegalArgumentException.class) to throw an IAE for nulls

[rymurr]

safer, less code and no change in behaviour! Im in!

@rdblue any comments?