minor #16749 [Form] Added getBlockPrefix() to ResolvedFormTypeInterface (webmozart)

This PR was merged into the 3.0-dev branch.

Discussion
----------

[Form] Added getBlockPrefix() to ResolvedFormTypeInterface

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

This is the follow-up PR to #16724.

If you call `$form->getConfig()->getType()`, all the methods of FormType should be usable. In that sense, ResolvedFormType is the developer-facing version of FormType.

It is true that the same could be achieved with `getInnerType()`, but that method should be used in edge cases only as it clutters the code and makes it confusing to read:

```php
$blockPrefix = $form->getConfig()->getType()->getInnerType()->getBlockPrefix();
```

Commits
-------

7e89345 [Form] Added getBlockPrefix() to ResolvedFormTypeInterface

src/Symfony/Component/Form/Extension/DataCollector/Proxy/ResolvedTypeDataCollectorProxy.php

@@ -43,20 +43,12 @@ class ResolvedTypeDataCollectorProxy implements ResolvedFormTypeInterface
         $this->dataCollector = $dataCollector;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getName()
-    {
-        return $this->proxiedType->getName();
-    }
-
     /**
      * {@inheritdoc}
      */
     public function getBlockPrefix()
     {
-        return method_exists($this->proxiedType, 'getBlockPrefix') ? $this->proxiedType->getBlockPrefix() : $this->getName();
+        return $this->proxiedType->getBlockPrefix();
     }
 
     /**

src/Symfony/Component/Form/ResolvedFormType.php

@@ -56,9 +56,7 @@ class ResolvedFormType implements ResolvedFormTypeInterface
     }
 
     /**
-     * Returns the prefix of the template block name for this type.
-     *
-     * @return string The prefix of the template block name
+     * {@inheritdoc}
      */
     public function getBlockPrefix()
     {

src/Symfony/Component/Form/ResolvedFormTypeInterface.php

@@ -20,6 +20,13 @@ use Symfony\Component\OptionsResolver\OptionsResolver;
  */
 interface ResolvedFormTypeInterface
 {
+    /**
+     * Returns the prefix of the template block name for this type.
+     *
+     * @return string The prefix of the template block name
+     */
+    public function getBlockPrefix();
+
     /**
      * Returns the parent type.
      *