Description

Because of usage of realpath in Symfony\Bridge\Doctrine\DependencyInjection\AbstractDoctrineExtension, entities from Phar-packages can't be loaded.

Steps to reproduce

1. Pack whole the framework with entities in Phar-package or just pack only own code into Phar.
2. Try to clear the cache or somehow use the entities-related features.
3. Say "hello" to Doctrine\Common\Persistence\MappingException with message File mapping drivers must have a valid directory path, however the given path seems to be incorrect!