feature #28669 [Serializer] Object class resolver (alanpoulain)

This PR was squashed before being merged into the 4.2-dev branch (closes #28669).

Discussion
----------

[Serializer] Object class resolver

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

When normalizing an object, it could be useful to use a custom method to resolve the class name of it instead of using `get_class`.
For instance, Doctrine is using proxy classes for lazy-loading and we usually want the real class and not the proxied one.
That's why we are using this trait in API Platform: https://github.com/api-platform/core/blob/master/src/Util/ClassInfoTrait.php
With this feature, we could solve an issue in API Platform with the JSON-LD normalizer when the eager fetching is disabled.

Commits
-------

18d2143 [Serializer] Object class resolver

src/Symfony/Component/Serializer/CHANGELOG.md

@@ -20,6 +20,8 @@ CHANGELOG
    either `NormalizerInterface` or `DenormalizerInterface`
  * deprecated creating a `Serializer` with encoders which do not implement
    either `EncoderInterface` or `DecoderInterface`
+ * added the optional `$objectClassResolver` argument in `AbstractObjectNormalizer`
+   and `ObjectNormalizer` constructor
 
 4.1.0
 -----

src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php

@@ -45,13 +45,14 @@ abstract class AbstractObjectNormalizer extends AbstractNormalizer
      * @var callable|null
      */
     private $maxDepthHandler;
+    private $objectClassResolver;
 
     /**
      * @var ClassDiscriminatorResolverInterface|null
      */
     protected $classDiscriminatorResolver;
 
-    public function __construct(ClassMetadataFactoryInterface $classMetadataFactory = null, NameConverterInterface $nameConverter = null, PropertyTypeExtractorInterface $propertyTypeExtractor = null, ClassDiscriminatorResolverInterface $classDiscriminatorResolver = null)
+    public function __construct(ClassMetadataFactoryInterface $classMetadataFactory = null, NameConverterInterface $nameConverter = null, PropertyTypeExtractorInterface $propertyTypeExtractor = null, ClassDiscriminatorResolverInterface $classDiscriminatorResolver = null, callable $objectClassResolver = null)
     {
         parent::__construct($classMetadataFactory, $nameConverter);
 
@@ -61,6 +62,7 @@ public function __construct(ClassMetadataFactoryInterface $classMetadataFactory
             $classDiscriminatorResolver = new ClassDiscriminatorFromClassMetadata($classMetadataFactory);
         }
         $this->classDiscriminatorResolver = $classDiscriminatorResolver;
+        $this->objectClassResolver = $objectClassResolver;
     }
 
     /**
@@ -87,7 +89,7 @@ public function normalize($object, $format = null, array $context = array())
         $data = array();
         $stack = array();
         $attributes = $this->getAttributes($object, $format, $context);
-        $class = \get_class($object);
+        $class = $this->objectClassResolver ? \call_user_func($this->objectClassResolver, $object) : \get_class($object);
         $attributesMetadata = $this->classMetadataFactory ? $this->classMetadataFactory->getMetadataFor($class)->getAttributesMetadata() : null;
 
         foreach ($attributes as $attribute) {
@@ -156,7 +158,7 @@ protected function instantiateObject(array &$data, $class, array &$context, \Ref
      */
     protected function getAttributes($object, $format = null, array $context)
     {
-        $class = \get_class($object);
+        $class = $this->objectClassResolver ? \call_user_func($this->objectClassResolver, $object) : \get_class($object);
         $key = $class.'-'.$context['cache_key'];
 
         if (isset($this->attributesCache[$key])) {

src/Symfony/Component/Serializer/Normalizer/ObjectNormalizer.php

@@ -30,13 +30,13 @@ class ObjectNormalizer extends AbstractObjectNormalizer
 {
     protected $propertyAccessor;
 
-    public function __construct(ClassMetadataFactoryInterface $classMetadataFactory = null, NameConverterInterface $nameConverter = null, PropertyAccessorInterface $propertyAccessor = null, PropertyTypeExtractorInterface $propertyTypeExtractor = null, ClassDiscriminatorResolverInterface $classDiscriminatorResolver = null)
+    public function __construct(ClassMetadataFactoryInterface $classMetadataFactory = null, NameConverterInterface $nameConverter = null, PropertyAccessorInterface $propertyAccessor = null, PropertyTypeExtractorInterface $propertyTypeExtractor = null, ClassDiscriminatorResolverInterface $classDiscriminatorResolver = null, callable $objectClassResolver = null)
     {
         if (!\class_exists(PropertyAccess::class)) {
             throw new LogicException('The ObjectNormalizer class requires the "PropertyAccess" component. Install "symfony/property-access" to use it.');
         }
 
-        parent::__construct($classMetadataFactory, $nameConverter, $propertyTypeExtractor, $classDiscriminatorResolver);
+        parent::__construct($classMetadataFactory, $nameConverter, $propertyTypeExtractor, $classDiscriminatorResolver, $objectClassResolver);
 
         $this->propertyAccessor = $propertyAccessor ?: PropertyAccess::createPropertyAccessor();
     }