minor #23633 [Form] Add some phpdocs for IDE autocompletion and better SCA (Koc)

This PR was merged into the 2.7 branch.

Discussion
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[Form] Add some phpdocs for IDE autocompletion and better SCA

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

@ogizanagi I've tryed add single phpdoc `@method FormInterface[] getIterator()` to `FormInterface` but it not works correctly in PHPStorm. Have you any ideas?

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Commits
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d30c751781 Add some phpdocs for IDE autocompletion and better SCA

src/Symfony/Component/Form/Extension/Core/EventListener/ResizeFormListener.php

@@ -15,6 +15,7 @@ use Symfony\Component\Form\FormEvents;
 use Symfony\Component\Form\FormEvent;
 use Symfony\Component\Form\Exception\UnexpectedTypeException;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+use Symfony\Component\Form\FormInterface;
 
 /**
  * Resize a collection form element based on the data sent from the client.
@@ -146,6 +147,7 @@ class ResizeFormListener implements EventSubscriberInterface
 
         if ($this->deleteEmpty) {
             $previousData = $event->getForm()->getData();
+            /** @var FormInterface $child */
             foreach ($form as $name => $child) {
                 $isNew = !isset($previousData[$name]);
 

src/Symfony/Component/Form/Extension/Core/Type/ChoiceType.php

@@ -120,6 +120,7 @@ class ChoiceType extends AbstractType
                 // Reconstruct the data as mapping from child names to values
                 $data = array();
 
+                /** @var FormInterface $child */
                 foreach ($form as $child) {
                     $value = $child->getConfig()->getOption('value');
 

src/Symfony/Component/Form/Extension/Validator/Constraints/FormValidator.php

@@ -83,6 +83,7 @@ class FormValidator extends ConstraintValidator
         } else {
             $childrenSynchronized = true;
 
+            /** @var FormInterface $child */
             foreach ($form as $child) {
                 if (!$child->isSynchronized()) {
                     $childrenSynchronized = false;