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

symfony/framework-bundle