Add missing return typehints to QueryNameGenerator

This will help to reduce static analysis warnings for consumers in apps baseline

Author: norkunas

src/Doctrine/Orm/Util/QueryNameGeneratorInterface.php

@@ -20,11 +20,15 @@ interface QueryNameGeneratorInterface
 {
     /**
      * Generates a cacheable alias for DQL join.
+     *
+     * @return literal-string
      */
     public function generateJoinAlias(string $association): string;
 
     /**
      * Generates a cacheable parameter name for DQL query.
+     *
+     * @return literal-string
      */
     public function generateParameterName(string $name): string;
 }