HV-828 Introducing ConstraintValidatorLocator to allow for a pluggable d...

...iscovery of additional constraint validator implementations.
Is there a specific reason for doing the annotation type determination via the initialize method?

Couldn't you just examine how the given validator class populates the first type parameter of `ConstraintValidator`? Similar to what we do in `TypeResolverBasedValueUnwrapper`. Should be a bit simpler and avoids the method filtering stuff.