Add missing autoload calls

Until either php 7.4 or doctrine/persistence 2 is required, these will
be needed to make sure php recognises signatures using the old names as
compatible with signatures using the new names.
This is necessary for types defined outside Symfony that extend types
from Symfony and still use the old names in signatures of methods they
override.

More details at https://dev.to/greg0ire/how-to-deprecate-a-type-in-php-48cf

Fixes doctrine/DoctrineMongoDBBundle#616

src/Symfony/Bridge/Doctrine/Form/Type/DoctrineType.php

@@ -285,3 +285,5 @@ public function reset()
         $this->choiceLoaders = [];
     }
 }
+
+interface_exists(ObjectManager::class);

src/Symfony/Bridge/Doctrine/Form/Type/EntityType.php

@@ -93,3 +93,5 @@ private function parameterToArray(Parameter $parameter)
         return [$parameter->getName(), $parameter->getType(), $parameter->getValue()];
     }
 }
+
+interface_exists(ObjectManager::class);

src/Symfony/Bridge/Doctrine/Security/User/EntityUserProvider.php

@@ -136,3 +136,6 @@ private function getClassMetadata(): ClassMetadata
         return $this->getObjectManager()->getClassMetadata($this->classOrAlias);
     }
 }
+
+interface_exists(ObjectManager::class);
+interface_exists(ObjectRepository::class);