…ormalization hierarchy (yceruto)

This PR was squashed before being merged into the 4.3-dev branch (closes #30371).

Discussion
----------

[OptionsResolver] Add a new method addNormalizer and normalization hierarchy

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #30310
| License       | MIT
| Doc PR        | symfony/symfony-docs#11103

### 3rd-party package

<details><summary>Given: (CLICK ME)</summary>
<p>

Generic type:
```php
class FooType extends AbstractType
{
    private $registry;

    public function __construct(ManagerRegistry $registry)
    {
        $this->registry = $registry;
    }

    // buildForm ...

    public function configureOptions(OptionsResolver $resolver): void
    {
        $resolver->setRequired('class');
        $resolver->setDefaults([
            'em' => null,
            'query' => null,
        ]);
        $resolver->setAllowedTypes('em', ['null', 'string']);
        $resolver->setAllowedTypes('query', ['null', 'callable']);

        $resolver->setNormalizer('em', function (Options $options, $em) {
            if (null !== $em) {
                return $this->registry->getManager($em);
            }

            return $this->registry->getManagerForClass($options['class']);
        });

        $resolver->setNormalizer('query', function (Options $options, $query) {
            if (\is_callable($query)) {
                $query = $query($options['em']->getRepository($options['class']));

                if (!$query instanceof Query) {
                    throw new UnexpectedTypeException($query, 'Doctrine\ORM\Query');
                }
            }

            return $query;
        });
    }
}
```
</p>
</details>

### App context

<details><summary>Before (CLICK ME)</summary>
<p>

Normalizing the new allowed value will require to override the parent's normalizer:
```php
class BarType extends AbstractType
{
    private $registry;

    public function __construct(ManagerRegistry $registry)
    {
        $this->registry = $registry;
    }

    // buildForm ...

    public function configureOptions(OptionsResolver $resolver): void
    {
        $resolver->addAllowedTypes('em', 'Doctrine\ORM\EntityManagerInterface');

        $resolver->setNormalizer('em', function (Options $options, $em) {
            if ($em instanceof EntityManagerInterface) {
                return $em;
            }

            if (null !== $em) {
                return $this->registry->getManager($em);
            }

            return $this->registry->getManagerForClass($options['class']);
        });

        $resolver->addAllowedTypes('query', 'string');

        $resolver->setNormalizer('query', function (Options $options, $query) {
            if (\is_callable($query)) {
                $query = $query($options['em']->getRepository($options['class']));

                if (!$query instanceof Query) {
                    throw new UnexpectedTypeException($query, 'Doctrine\ORM\Query');
                }
            }

            if (\is_string($query)) {
                $query = $options['em']->createQuery($query);
            }

            return $query;
        });
    }

    public function getParent()
    {
        return FooType::class;
    }
}
```
</p>
</details>

<details><summary>After (CLICK ME)</summary>
<p>

The new normalizer is added to the stack and it'll receive the previously normalized value or if `forcePrepend = true` the validated value:
```php
class BarType extends AbstractType
{
    // buildForm ...

    public function configureOptions(OptionsResolver $resolver): void
    {
        $resolver->addAllowedTypes('em', 'Doctrine\ORM\EntityManagerInterface');

        $resolver->addNormalizer('em', function (Options $options, $em) {
            if ($em instanceof EntityManagerInterface) {
                return $em;
            }

            return $em;
        }, true); // $forcePrepend = true (3rd argument)

        $resolver->addAllowedTypes('query', 'string');

        $resolver->addNormalizer('query', function (Options $options, $query) {
            if (\is_string($query)) {
                $query = $options['em']->createQuery($query);
            }

            return $query;
        });
    }

    public function getParent()
    {
        return FooType::class;
    }
}
```
</p>
</details>

Commits
-------

cf41254 [OptionsResolver] Add a new method addNormalizer and normalization hierarchy

…od (yceruto)

This PR was merged into the master branch.

Discussion
----------

[OptionsResolver] Documenting the new addNormalizer method

symfony/symfony#30371

Commits
-------

a2e6c2a Documenting the new method addNormalizer in OptionsResolver component

…nd (yceruto)

This PR was merged into the 4.3-dev branch.

Discussion
----------

[Form] Show all option normalizers on debug:form command

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

Follow-up #30371

![normalizers](https://user-images.githubusercontent.com/2028198/55996454-6667df80-5c85-11e9-94f6-9ee3988833f3.png)

Commits
-------

f1d3bc0 Show all option normalizers on debug:form command