Merge branch '3.3' into 3.4

* 3.3:
  PHP CS Fixer: clean up repo and adjust config
  use interface_exists instead of class_exists
  Dumper shouldn't use html format for phpdbg
  [Validator] Fix access to root object when using composite constraint

Author: nicolas-grekas

Command/ServerLogCommand.php

@@ -39,7 +39,7 @@ public function isEnabled()
         }
 
         // based on a symfony/symfony package, it crashes due a missing FormatterInterface from monolog/monolog
-        if (!class_exists(FormatterInterface::class)) {
+        if (!interface_exists(FormatterInterface::class)) {
             return false;
         }