Check if core's assumptions for loading data fields is correct or not

How $data_fields are loaded in \Drupal\Core\Entity\Sql\SqlContentEntityStorage::attachPropertyData looks a bit strange. Because what if you have a revisionable and translatable entity, where some base fields only live on the data table (i.e. that field is not revisionable nor translatable), then that field won't be attached.

I think we need to add in fields from the data table in some cases.