minor #16500 [Form] Update choice_loader.rst.inc (issamkhadiri1989)

This PR was submitted for the 6.0 branch but it was squashed and merged into the 5.4 branch instead.

Discussion
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[Form] Update choice_loader.rst.inc

Hello,
I think it is better to extend the class `ConstantsType` from the `Form\AbstractTypeExtension` instead. As we're using the function `getExtendedTypes` i think it might be better. This method is available in the `AbstractTypeExtension`  class and not in the `AbstractType` class. I might be wrong but here we're about to create a type extension from the ChoiceType.

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Commits
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dab392b [Form] Update choice_loader.rst.inc

Author: javiereguiluz

reference/forms/types/options/choice_loader.rst.inc

@@ -42,9 +42,9 @@ better performance::
 
     class ConstantsType extends AbstractType
     {
-        public static function getExtendedTypes(): iterable
+        public function getParent(): string
         {
-            return [ChoiceType::class];
+            return ChoiceType::class;
         }
 
         public function configureOptions(OptionsResolver $resolver)