… (lyrixx)

This PR was merged into the 4.1-dev branch.

Discussion
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[Serializer] Added a ConstraintViolationListNormalizer

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11309
| License       | MIT
| Doc PR        | -

---

It seems logical to me that Symfony is able to serialise natively some very common Symfony data structure. (and requested by @nicolas-grekas & @javiereguiluz )

Usage example (from symfony/symfony-demo):

```php
    /**
     * @route("", name="api_blog_new")
     * @method("POST")
     * @Security("is_granted('ROLE_ADMIN')")
     */
    public function newAction(Request $request)
    {
        $data = $request->getContent();

        $post = $this->get('serializer')->deserialize($data, Post::class, 'json', ['groups' => ['post_write']]);

        $post->setAuthor($this->getUser());

        $violations = $this->get('validator')->validate($post);

        $post->setSlug($this->get('slugger')->slugify($post->getTitle()));

        if (count($violations) > 0) {
            $repr = $this->get('serializer')->serialize($violations, 'json');

            return JsonResponse::fromJsonString($repr, 400);
        }

        $this->getDoctrine()->getManager()->persist($post);
        $this->getDoctrine()->getManager()->flush();

        $repr = $this->get('serializer')->serialize($post, 'json', ['groups' => ['post_read']]);

        return JsonResponse::fromJsonString($repr);
    }
```

Commits
-------

2a35d09 [Serializer] Added a ConstraintViolationListNormalizer