…sable auto-validation (dunglas)

This PR was squashed before being merged into the 4.4 branch (closes #32107).

Discussion
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[Validator] Add AutoMapping constraint to enable or disable auto-validation

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #32070, #32015   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | todo

As discussed in #32070 and #32015, it's sometimes mandatory to prevent some classes or properties to be auto mapped (auto-validated). This PR introduces a new constraint, `@AutoMapping` allowing to do exactly that. Examples:

Class:

```php
use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Constraints as Assert;

/**
 * @Orm\Entity
 * @Assert\AutoMapping(false)
 */
class DoctrineLoaderNoAutoMappingEntity
{
    /**
     * @Orm\Id
     * @Orm\Column
     */
    public $id;

    /**
     * @Orm\Column(length=20, unique=true)
     */
    public $maxLength;
}
```

Property:

```php
namespace Symfony\Bridge\Doctrine\Tests\Fixtures;

use Doctrine\ORM\Mapping as ORM;
use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
use Symfony\Component\Validator\Constraints as Assert;

/**
 * @Orm\Entity
 */
class DoctrineLoaderEntity extends DoctrineLoaderParentEntity
{
    /**
     * @Orm\Id
     * @Orm\Column
     */
    public $id;

    /**
     * @Orm\Column(length=10)
     * @Assert\AutoMapping(false)
     */
    public $noAutoMapping;
}
```

The rules are the following:

* If the constraint is present on a property, and set to true, auto-mapping is always on, regardless of the config, and of any class level annotation
* If the constraint is present on a property, and set to false, auto-mapping is always off, regardless of the config, and of any class level annotation
* If the constraint is present on a class, and set to true, auto-mapping is always on except if a the annotation has been added to a specific property, and regardless of the config
* If the constraint is present on a class, and set to false, auto-mapping is always off except if a the annotation has been added to a specific property, and regardless of the config

Commits
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f6519ce [Validator] Add AutoMapping constraint to enable or disable auto-validation