[DI] Fix DefinitionDecorator existency for composer authoritative+IDEs

Author: nicolas-grekas

DefinitionDecorator.php

@@ -13,11 +13,17 @@
 
 @trigger_error('The '.__NAMESPACE__.'\DefinitionDecorator class is deprecated since version 3.3 and will be removed in 4.0. Use the Symfony\Component\DependencyInjection\ChildDefinition class instead.', E_USER_DEPRECATED);
 
+class_exists(ChildDefinition::class);
+
+return;
+
 /**
  * This definition decorates another definition.
  *
  * @author Johannes M. Schmitt <schmittjoh@gmail.com>
  *
  * @deprecated The DefinitionDecorator class is deprecated since version 3.3 and will be removed in 4.0. Use the Symfony\Component\DependencyInjection\ChildDefinition class instead.
  */
-class_exists(ChildDefinition::class);
+class DefinitionDecorator extends Definition
+{
+}