Issue #2941062 by plach, Wim Leers: EntityUntranslatableFieldsConstraintValidator always allows changes in default revisions

Issue #2878556 by plach, matsbla, vijaycs85, Gábor Hojtsy, catch, gabesullice, effulgentsia, hchonov, hass, amateescu, xjm: Ensure that changes to untranslatable fields affect only one translation in pending revisions