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/http-kernel/CacheWarmer/WarmableInterface.php

@@ -21,7 +21,7 @@ interface WarmableInterface
     /**
      * Warms up the cache.
      *
-     * @param string $cacheDir The cache directory
+     * @return string[] A list of classes or files to preload on PHP 7.4+
      */
-    public function warmUp($cacheDir);
+    public function warmUp(string $cacheDir);
 }