[Serializer] Added a ConstraintViolationListNormalizer

[javiereguiluz]

symfony/symfony#22150

It normalizes ConstraintViolationListInterface instances according to RFC7807.

[javiereguiluz]

We need a volunteer to contribute these docs. Someone expert in the Serializer component: @dunglas, @lyrixx, @Simperfit? Thanks!

[lyrixx]

Should we really document it ? I mean, it's just about doing $this->serializer->serialize($errors);

[javiereguiluz]

I think you are right. In the future we may add some brief mention somewhere if we think it's necessary. Thanks!

[dunglas]

We should at least add it to the list of available normalizers. People using directly the component have no way to discover this feature.

[javiereguiluz]

Let's reopen then. But we'll need a volunteer to do this. Thanks!

[javiereguiluz]

Fixed by #9855.