[WIP] Untyped dictionary serializer

[aloneguid]

Use single codebase from FSC/FAC to understand untyped dictionaries. This will deprecate row API when absolutely stable.

Motivation

1. Single codebase for class serializer and untyped dictionary serializer.
2. De-serialization produces JSON-like structures in memory. These can be written back to JSON file as is.
3. Row API is an old legacy that is somewhat buggy and very hard to evolve and fix.

Release plan

This will be released as an addition to the current class serializer in v4. Row API methods will be marked as deprecated and eventually removed in v5, making it a primary dynamic API.

Todo

• Atomic fields.
• Nullable atomic fields.
• Maps.
• Structs.
• Lists.
  • Atomics
  • Lists and Structs
• Public interface refinement.
• WRS docs restructure and documenting the above.
• Add docs for [ParquetRequired] (related to the above).