Platform library should expose Entity Representation flattening-related functions

[jakedoublev]

Background

As a result of the accepted ADR to employ flattening of an Entity Representation into known fields and values, the platform needs a small library of functions to do flattening and comparison.

Acceptance Criteria

This set of functions, consumable downstream in PEPs or tools like otdfctl:

1. Take arbitrary JSON and flatten it into an array of fields and values (see existing proto, and ADR example). Every array value should appear twice in the output, once with the index wildcard as * and once with the index specified numerically. This gives admins the ability to entitle based on order in an array or presence without the platform driving that opinion.
2. Take an Entity Representation and a flattened set of fields and values and compare to find the matched field/value pairs.
3. Take an Entity Representation and a set of selected fields and provide the values for whichever are present, even if they differ

Unit tests for all of the above.