Allow overide of CsvEncoder::AS_COLLECTION_KEY in context

[Stav88]

API Platform version(s) affected: 3.4.1 (seems on main branch by analaysing code)

Description
denormalizationContext CsvEncoder::AS_COLLECTION_KEY is erased by API platforme when defined on a route operation.

How to reproduce

• Entity

  #[ApiResource(
      operations: [
          new Patch(
              uriTemplate: '/admin/books{._format}',
              processor: MultipleBookPersistProcessor::class,
              formats: ['csv' => ['text/csv']],
              validate: false,
              denormalizationContext: [
                  CsvEncoder::AS_COLLECTION_KEY => true, // say to CsvEncoder to output a collection
                  'deserializer_type' => self::class . '[]', // say to symfony to use ArrayDenormalizer
              ]
          ),
      ]
  )]
  class Book {...}
  

• Processor to support an array of entity

  class MultipleBookPersistProcessor implements ProcessorInterface
  {
      public function __construct(
          private BookPersistProcessor $bookPersistProcessor,
      ) {
      }
  
      public function process(mixed $data, Operation $operation, array $uriVariables = [], array $context = [])
      {
          foreach ($data as $book) {
              $this->bookPersistProcessor->process($book, $operation, $uriVariables, $context);
          }
      }
  }
  

• Try to patch a CSV :
  • Multi line CSV (OK) :

    book,title,author,condition
    https://openlibrary.org/books/OL2055137M.json,Hyperion,"Dan Simmons",https://schema.org/NewCondition
    https://openlibrary.org/books/OL28276567M.json,Hyperion 2,"Dan Simmons",https://schema.org/NewCondition
    

  • One line CSV (fail) :

    book,title,author,condition
    https://openlibrary.org/books/OL2055137M.json,Hyperion,"Dan Simmons",https://schema.org/NewCondition
    

Possible Solution
In src/Serializer/SerializerContextBuilder.php , it would be better set $context[CsvEncoder::AS_COLLECTION_KEY] only if it has not been set to allow override :

$context[CsvEncoder::AS_COLLECTION_KEY] = $context[CsvEncoder::AS_COLLECTION_KEY] ?? false;

Additional Context
See comment on this old PR : https://github.com/api-platform/core/pull/3009/files#r342574912