DATACMNS-511 - Improve equals(…) and hashCode() in TypeVariableTypeInformation.

The equals(…) and hashCode() methods of TypeVariableTypeInformation previously tried to evaluate the unresolved context of the type variable. This can cause issues in recursive type definitions as set up in the according test case. We now implement the methods based on the resolved type to makes sure we break the recursive lookup of PersistentEntity instances in AbstractMappingContext. 

The erroneous lookup was actually caused by unresolved base types being added to the mapping context within the JPA project as the JPA meta-model also returns those types as managed types.

Related pull request: #84.