Merge branch '5.3' into 5.4

* 5.3:
  [Cache] Add missing return type
  [5.2] Add missing `@return` annotations
  [4.4] Add missing `@return` annotations
  Handle lock with long key
  #42227 update phpdoc to recommend createIndex over ensureIndex

Author: nicolas-grekas

Loader/Configurator/AbstractConfigurator.php

@@ -41,6 +41,9 @@ public function __call(string $method, array $args)
         throw new \BadMethodCallException(sprintf('Call to undefined method "%s::%s()".', static::class, $method));
     }
 
+    /**
+     * @return array
+     */
     public function __sleep()
     {
         throw new \BadMethodCallException('Cannot serialize '.__CLASS__);