Allow reusing of the MediaType for other correctly interfaced media o…

…bjects (#2313)

The default value for data_class is set to `$this->class` already and it is configurable, allowing override improved reusability without breaking anything.

src/Form/Type/MediaType.php

@@ -50,7 +50,7 @@ public function __construct(Pool $pool, string $class)
 
     public function buildForm(FormBuilderInterface $builder, array $options): void
     {
-        $dataTransformer = new ProviderDataTransformer($this->pool, $this->class, [
+        $dataTransformer = new ProviderDataTransformer($this->pool, $options['data_class'], [
             'provider' => $options['provider'],
             'context' => $options['context'],
             'empty_on_new' => $options['empty_on_new'],