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/event-dispatcher/EventSubscriberInterface.php

@@ -43,7 +43,7 @@ interface EventSubscriberInterface
      * The code must not depend on runtime state as it will only be called at compile time.
      * All logic depending on runtime state must be put into the individual methods handling the events.
      *
-     * @return array The event names to listen to
+     * @return array<string, string|array{0: string, 1: int}|list<array{0: string, 1?: int}>>
      */
     public static function getSubscribedEvents();
 }