Add stub for GenericEvent (#135)

Author: emodric

extension.neon

@@ -24,6 +24,7 @@ parameters:
 		- stubs/FormTypeExtensionInterface.stub
 		- stubs/FormTypeInterface.stub
 		- stubs/FormView.stub
+		- stubs/GenericEvent.stub
 		- stubs/HeaderBag.stub
 		- stubs/Node.stub
 		- stubs/NormalizableInterface.stub

stubs/GenericEvent.stub

@@ -0,0 +1,11 @@
+<?php
+
+namespace Symfony\Component\EventDispatcher;
+
+/**
+ * @implements \IteratorAggregate<string, mixed>
+ */
+class GenericEvent implements \IteratorAggregate
+{
+
+}