Re-factor on top of Changed Fields API module if possible

Problem/Motivation

We are stealing a key informative method from Changed Fields API module, we should make an honest module of it and make it a dependency and use its API.

See 💬 Any functionality (or examples or advice) for comparing multivalue fields? Active for details.

Proposed resolution

Plan A: Refactor to use the Changed Fields API.
Plan B: If not possible, even with achievable changes to Changed Fields API, propose sharing custody of the comparable properties list, possibly in a third utility module that other modules could also call on (and extend in a consistent way).

Remaining tasks

1. Confirm that we can get the current delta for each field value
2. Try to predict any other possible limitations of the API that need to be addressed pre-emptively.
3. Re-factor on the Changed Fields API.

User interface changes

API changes

Data model changes