Issue #2821077 by Wim Leers, dawehner, tedbow, amateescu, tstoeckler,...

Issue #2821077 by Wim Leers, dawehner, tedbow, amateescu, tstoeckler, alexpott: PATCHing entities validates the entire entity, also unmodified fields, so unmodified fields can throw validation errors

(cherry picked from commit 73769ef5)