Issue #2454649 by Aki Tendo, dawehner: Cache Optimization and hardening -- [PP-1] Use assert() instead of exceptions in Cache::merge(Tags|Contexts)

Issue #2512718 by Berdir, pfrenssen, Wim Leers, Fabianx, dawehner, catch, effulgentsia, plach, Gábor Hojtsy: EntityManager::getTranslationFromContext() should add the content language cache context to the entity

Issue #2143729 by tstoeckler, plach, jsbalsera, Berdir, mauzeh, damiankloip, andypost: Entity definitions miss a language entity key

Issue #2340667 by YesCT, Pedro Lozano, alexpott, martin107: Protect Drupal\Core\Language\Language::id, and use getId().

Issue #2304987 by Berdir, Wim Leers: Fixed Don't invalidate cache tags of referenced entities, use entity list cache tags correctly, add test coverage for entity list cache tags.

Issue #2340123 by Wim Leers: Setting cache tags can be tricky: use strings instead of nested arrays to improve DX.

Issue #2154435 by andypost, Berdir, mparker17: Rename EntityAccessController to EntityAccessControlHandler.

Issue #697760 by sun: Replace getInfo() in tests with native phpDoc + annotations (following PHPUnit).

Issue #2190313 by pfrenssen, Berdir, amateescu, ianthomas_uk: Add $EntityType::load() and loadMultiple() to simplify loading entities.

Issue #2217749 by Wim Leers, Jalandhar, visabhishek, damiankloip: Entity base class should provide standardized cache tags and built-in invalidation.