Merge branch '4.4'

* 4.4:
  [Mailer] simplified the way TLS/SSL/StartTls work
  [VarDumper] Add test dump image
  Allow exchange type headers binding
  Add types to private and final methods.
  [Messenger] InMemoryTransport handle acknowledged and rejected messages
  [Intl] Validate region preferred alpha code mapping
  Added ErrorHandler::call() method utility to turns any PHP warnings into `\ErrorException`
  [Intl] Full alpha3 language support
  [Monolog] Added ElasticsearchLogstashHandler

Author: fabpot

Filesystem.php

@@ -705,7 +705,10 @@ private function getSchemeAndHierarchy(string $filename): array
         return 2 === \count($components) ? [$components[0], $components[1]] : [null, $components[0]];
     }
 
-    private static function box($func)
+    /**
+     * @return mixed
+     */
+    private static function box(callable $func)
     {
         self::$lastError = null;
         set_error_handler(__CLASS__.'::handleError');