Saem Ghani your last comment does not really provide any rationale behind extraction of the remaining methods into an interface. There's no advantage in extracting those methods to an own interface. createQueryBuilder, createResultSetMappingBuilder, createNamedQuery, createNativeNamedQuery, clear, __call, getEntityManager, getClassMetadata are all utility methods that are not good candidates for an interface. You can easily re-implement those on an existing entity manager.
Just use the Doctrine\Common\Persistence\ObjectRepository API: you should actually stick to that to increase portability across the various object managers in doctrine project.
If you need all those methods too, you are looking for inheritance, not composition (and probably are delegating too much responsibility to the repository).