Issue #2779931 by Sam152, alexpott, timmillwood, Wim Leers, catch, dawehner:...

Issue #2779931 by Sam152, alexpott, timmillwood, Wim Leers, catch, dawehner: Add storage exception that enforces unique content_entity_type_id and content_entity_id on the content moderation state content entity, and add access control handler to forbid all access