Issue #2443409 by Berdir: Add a way to entity manager to get fresh entity and field definitions without invalidating all caches

Issue #2398689 by jeqq: Follow-up: Applying entity schema updates still fails when both field and entity type definitions changes

Issue #2342543 by fago, dixon_, jeqq: Applying entity schema updates fail when both entity type and base field definitions change at the same time

Issue #2100343 by Berdir, fago, martin107, visabhishek, sriharsha.uppuluri, Yorirou: Remove 'fieldable' key in entity definitions in favour of 'field_ui_base_route'.

Issue #2337927 by effulgentsia, plach, fago: Fixed SqlContentEntityStorage::onFieldStorageDefinition(Create|Update|Delete)() is broken for base fields.

Issue #2333113 by effulgentsia, plach: Add an EntityDefinitionUpdateManager so that entity handlers can respond (e.g., by updating db schema) to code updates in a controlled way (e.g., from update.php).