Alternative moderation_state field widgets do not receive the same access/visibility treatment as the default ModerationStateWidget.

Problem/Motivation

Currently we add a base field to entity types and then hide the moderation_state widget if the specific entity we are editing isn't being moderated. Some bundles may have moderation switched off. The way we do this is with a check in our widget, but this doesn't protect other widgets and can cause a fatal with the following steps:

1. drush si standard && drush en content_moderation
2. Edit the Article form display, change the widget to "Textfield".
3. Save any article, see a fatal.

Proposed resolution

Use field access for controlling if the field should appear or not.

Remaining tasks

User interface changes

API changes

Data model changes