LogEntry::getPerformer returns a User. UserIdentity should be enough. ManualLogEntry already has getPerformerIdentity - it should just be elevated to the interface and implemented in DatabaseLogEntry. Replace all usages, hard-deprecate.
Additionally, DatabaseLogEntry should use ActorNormalization::getActorById on $row->log_actor only - log_user and user_name fields were deleted from MW database in favor of log_actor, so the getPerformer method can be vastly simplified. Same with RCDatabaseLogEntry::getPerformer
Change 664912 abandoned by Vadim Kovalenko:
[mediawiki/extensions/TranslationNotifications@master] Avoid using LogEntry::getPerformer in favor of getPerformerIdentity
Fix replaced to separate branch - https://gerrit.wikimedia.org/r/c/mediawiki/extensions/TranslationNotifications/ /665639