migration symfony 5 4 (#300)

* symfony 5.4 (diff dev)

* symfony 5.4 (working)

* symfony 5.4 (update autoload)

* symfony 5.4 (remove swiftmailer mailer implementation)

* symfony 5.4 (php doc and split Global accessor class)


### Impacted packages:

composer require php:">=7.2.5 <8.0.0" symfony/console:5.4.* symfony/dotenv:5.4.* symfony/framework-bundle:5.4.* symfony/twig-bundle:5.4.* symfony/yaml:5.4.* --update-with-dependencies

composer require symfony/stopwatch:5.4.* symfony/web-profiler-bundle:5.4.* --dev --update-with-dependencies

lib/symfony/console/Helper/HelperInterface.php

@@ -26,14 +26,14 @@ interface HelperInterface
     /**
      * Gets the helper set associated with this helper.
      *
-     * @return HelperSet A HelperSet instance
+     * @return HelperSet|null
      */
     public function getHelperSet();
 
     /**
      * Returns the canonical name of this helper.
      *
-     * @return string The canonical name
+     * @return string
      */
     public function getName();
 }