feature #19197 [Serializer][FrameworkBundle] Add a CSV encoder (dunglas)

This PR was squashed before being merged into the 3.2-dev branch (closes #19197).

Discussion
----------

[Serializer][FrameworkBundle] Add a CSV encoder

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

Usage:

```php
use Symfony\Component\Serializer\Serializer;
use Symfony\Component\Serializer\Encoder\CsvEncoder;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;

$serializer = new Serializer(array(new ObjectNormalizer()), array(new CsvEncoder()));
// or $serializer = $container->get('serializer'); when using the full stack framework
$serializer->encode($something, 'csv');
$serializer->decode(<<<'CSV'
id,name
1,Kévin
CSV
, 'csv');
```

CSV files must contain a header line with property names as keys.

ping @clementtalleu @Simperfit @gorghoa

Commits
-------

e71f5be [Serializer][FrameworkBundle] Add a CSV encoder

Author: fabpot

DependencyInjection/FrameworkExtension.php

@@ -27,6 +27,7 @@
 use Symfony\Component\Config\FileLocator;
 use Symfony\Component\PropertyAccess\PropertyAccessor;
 use Symfony\Component\Serializer\Encoder\YamlEncoder;
+use Symfony\Component\Serializer\Encoder\CsvEncoder;
 use Symfony\Component\Serializer\Mapping\Factory\CacheClassMetadataFactory;
 use Symfony\Component\Serializer\Normalizer\DataUriNormalizer;
 use Symfony\Component\Serializer\Normalizer\DateTimeNormalizer;
@@ -1045,6 +1046,12 @@ private function registerSerializerConfiguration(array $config, ContainerBuilder
             $definition->addTag('serializer.encoder');
         }
 
+        if (class_exists(CsvEncoder::class)) {
+            $definition = $container->register('serializer.encoder.csv', CsvEncoder::class);
+            $definition->setPublic(false);
+            $definition->addTag('serializer.encoder');
+        }
+
         $loader->load('serializer.xml');
         $chainLoader = $container->getDefinition('serializer.mapping.chain_loader');