feature #16747 [Form] Improved performance of ChoiceType and its subtypes (webmozart)

This PR was merged into the 2.7 branch.

Discussion
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[Form] Improved performance of ChoiceType and its subtypes

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

I found out today that, although CachingFactoryDecorator is part of Symfony 2.7, it is not configured to be used in the DI configuration. This simple in-memory cache improved the page load by 50% for one considerably large form with many (~600) choice/entity fields that I was working on today.

Also, caching of query builders with parameters was broken, since the parameters are represented by objects. PHP's object hashes were used to calculate the cache keys, hence the cache always missed. I converted parameters to arrays for calculating the cache keys to fix this problem.

Commits
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a0ef101 [Form] Improved performance of ChoiceType and its subtypes

Author: Tobion

Extension/Core/Type/ChoiceType.php

@@ -12,6 +12,7 @@
 namespace Symfony\Component\Form\Extension\Core\Type;
 
 use Symfony\Component\Form\AbstractType;
+use Symfony\Component\Form\ChoiceList\Factory\CachingFactoryDecorator;
 use Symfony\Component\Form\ChoiceList\Factory\PropertyAccessDecorator;
 use Symfony\Component\Form\ChoiceList\LegacyChoiceListAdapter;
 use Symfony\Component\Form\ChoiceList\View\ChoiceGroupView;
@@ -46,7 +47,11 @@ class ChoiceType extends AbstractType
 
     public function __construct(ChoiceListFactoryInterface $choiceListFactory = null)
     {
-        $this->choiceListFactory = $choiceListFactory ?: new PropertyAccessDecorator(new DefaultChoiceListFactory());
+        $this->choiceListFactory = $choiceListFactory ?: new CachingFactoryDecorator(
+            new PropertyAccessDecorator(
+                new DefaultChoiceListFactory()
+            )
+        );
     }
 
     /**