Provide a portable way to identify the 'direction' of bean validation failures

CXF user pointed to the fact that there's no portable way to get a custom ConstraintValidationException mapper recognize whether an exception occurred during the request or response validation.
#### Affected Versions
[2.0]

Start by reviewing the Jakarta REST integration with Bean Validation and the ConstraintValidationException mapper described in the issue. Trace how request and response validation failures reach a custom mapper, then determine what portable direction information the API would need and how completion would be verified across both validation paths.

Written by the indexing model from the issue text.