Add the option to restrict editing of existing field values (but still allow adding new values)

Problem/Motivation

Value revisions is especially useful with multivalue fields, and makes it possible in Drupal to restrict editing of existing field values but still allow adding new values.

This is related to but less ambitious than ✨ Permissions to control who can edit or delete value revisions Active as we would not be basing edit ability on whether it was one own's submitted value or not; once it is saved it becomes part of the record content editors will have control over but contributors will not.

Proposed resolution

Make a permission that allows users to:

Change existing values in fields with Field Value Revisions enabled: By default, Field Value Revisions Control will lock the ability of people who can otherwise edit content from changing existing field values, limiting them to only adding new values. Give this permission to roles that should be able to edit existing values as well as add new ones (to multivalue fields).

Remaining tasks

User interface changes

API changes

Data model changes