HV-828 Introducing ConstraintDefinitionContributor to allow for a plugga...

...ble discovery of additional constraint validator implementations.

* Added the suggested builder pattern
* Aligned names/packages to refer to constraint definitions
You don't even have to loop the interfaces. This should suffice:

    ResolvedType resolvedType = typeResolver.resolve( constraintValidatorClass );
    return resolvedType.typeParametersFor( ConstraintValidator.class ).get( 0 ).getErasedType();