Skip wasteful term update index queuing

[rinatkhaziev]

Don't push posts to queue on a term update if 'name', 'slug', 'parent', 'term_taxonomy_id' are not modified during the update.

Description

Currently, the SyncManager operates on edited_term, unfortunately, even a simple wp_update_term that doesn't have any field update triggers the hook, so potentially anyone can go to the term edit screen, hit update, and cause a full re-index of documents with that term, which is not ideal.

This PR aims to address that with a bit of hackery:

1. First on edit_terms - that happens PRIOR the term update we store the term
2. Second, on edited_terms we fetch the new term and compare to the previously stored.
3. Only index if the term was actually updated .
4. Profit

Checklist

Please make sure the items below have been covered before requesting a review:

• [ ] This change works and has been tested locally (or has an appropriate fallback).
• [ ] This change works and has been tested on a Go sandbox.
• [ ] This change has relevant unit tests (if applicable).
• [ ] This change has relevant documentation additions / updates (if applicable).
• [ ] This change has the fix PRed upstream (if applicable). If not applicable, it has the relevant "// VIP: reason for the discrepancy with upstream" comment in places where the code is discrepant.

Steps to Test

[rinatkhaziev]

Closing in favor of the above-linked PR.

[rinatkhaziev]

Although this may approach may be desirable in ElasticPress upstream too, so not deleting the branch for now.