minor symfony#18303 [Form] Fix Forms docblock to use FQCN (HeahDude)

This PR was merged into the 2.8 branch.

Discussion
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[Form] Fix `Forms` docblock to use FQCN

| Q             | A
| ------------- | ---
| Branch?       | 2.8+
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | -

Commits
-------

df61aab [Form] Fix `Forms` docblock to use FQCN

Author: Tobion

src/Symfony/Component/Form/Forms.php

@@ -24,11 +24,12 @@
  * $formFactory = Forms::createFormFactory();
  *
  * $form = $formFactory->createBuilder()
- *     ->add('firstName', 'text')
- *     ->add('lastName', 'text')
- *     ->add('age', 'integer')
- *     ->add('gender', 'choice', array(
- *         'choices' => array('m' => 'Male', 'f' => 'Female'),
+ *     ->add('firstName', 'Symfony\Component\Form\Extension\Core\Type\TextType')
+ *     ->add('lastName', 'Symfony\Component\Form\Extension\Core\Type\TextType')
+ *     ->add('age', 'Symfony\Component\Form\Extension\Core\Type\IntegerType')
+ *     ->add('gender', 'Symfony\Component\Form\Extension\Core\Type\ChoiceType', array(
+ *         'choices' => array('Male' => 'm', 'Female' => 'f'),
+ *         'choices_as_values' => true,
  *     ))
  *     ->getForm();
  * </code>