[TypeDeclaration] Add ReturnTypeFromGetRepositoryDocblockRector

[TomasVotruba]

Adds ReturnTypeFromGetRepositoryDocblockRector.

Moves a @return docblock type into a native return type when a method's sole return is an EntityManagerInterface::getRepository() fetch.

 final class EventModel
 {
     public function __construct(private \Doctrine\ORM\EntityManagerInterface $em)
     {
     }

-    /**
-     * @return \Mautic\CampaignBundle\Entity\EventRepository
-     */
-    public function getRepository()
+    public function getRepository(): \Mautic\CampaignBundle\Entity\EventRepository
     {
         return $this->em->getRepository(Event::class);
     }
 }

Guards

• skips if a native return type is already present
• exactly one scoped return, whose expr is a getRepository() method call
• caller must be (or implement) Doctrine\ORM\EntityManagerInterface
• @return must resolve to a plain, existing class (ReflectionProvider::hasClass); generic / non-existing types are skipped
• ClassMethodReturnTypeOverrideGuard prevents breaking parent/child signatures
• the now-redundant @return tag is removed