HV-2018 Keep the interface if it is the hierarchy root

[marko-bekhta]

https://hibernate.atlassian.net/browse/HV-2018

I guess we never anticipated that the validation constraints will be only defined on an interface and that interface is passed to the validateValue().
What currently happens is that beanMetaData.getClassHierarchy() is empty and once we want to validate things we never get into this loop:

hibernate-validator/engine/src/main/java/org/hibernate/validator/internal/engine/ValidatorImpl.java

Lines 458 to 462 in bb61299

	// evaluating the constraints of a bean per class in hierarchy, this is necessary to detect potential default group re-definitions
	for ( Class<? super U> clazz : beanMetaData.getClassHierarchy() ) {
	BeanMetaData<? super U> hostingBeanMetaData = beanMetaDataManager.getBeanMetaData( clazz );
	boolean defaultGroupSequenceIsRedefined = hostingBeanMetaData.isDefaultGroupSequenceRedefined();

Which means we actually do not evaluate any constraints...

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[marko-bekhta]

@gsmet I'll let you take a look at this one once you have time. I think the patch makes sense, but maybe I'm missing something.. and since the filtering part should only happen once when the metadata is created it shouldn't cause issues because of those additional allocations to create filter instances.