merged branch Tobion/form-phpdoc (PR #8925)

This PR was merged into the 2.3 branch.

Discussion
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[Form] fix iterator phpdoc

It returns IteratorAggregate. But we probably only want to specify Traversable because that is was counts.

Fix from #8852

Commits
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f438ac3 [Form] fix iterator typehint

src/Symfony/Component/Form/Form.php

@@ -938,7 +938,7 @@ class Form implements \IteratorAggregate, FormInterface
     /**
      * Returns the iterator for this group.
      *
-     * @return \Iterator
+     * @return \Traversable
      */
     public function getIterator()
     {