Issue #2810355 by joseph.olstad, Leksat, ravi.shankar, Berdir, jungle,...

Issue #2810355 by joseph.olstad, Leksat, ravi.shankar, Berdir, jungle, suranga.gamage, adityasingh, benjifisher, Jelle_S, alexpott, Wim Leers, xjm, smustgrave, catch, hchonov, star-szr, webchick, wluisi, dawehner, daffie, cilefen: $entity->isDefaultTranslation() behaves incorrectly when changing default translation, causing file/image field usage to be set to zero, causing files to be deleted

(cherry picked from commit aa3ecb2c)