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/config/Definition/Builder/NormalizationBuilder.php

@@ -30,12 +30,12 @@ class NormalizationBuilder
     /**
      * Registers a key to remap to its plural form.
      *
-     * @param string $key    The key to remap
-     * @param string $plural The plural of the key in case of irregular plural
+     * @param string      $key    The key to remap
+     * @param string|null $plural The plural of the key in case of irregular plural
      *
      * @return $this
      */
-    public function remap($key, $plural = null)
+    public function remap(string $key, string $plural = null)
     {
         $this->remappings[] = [$key, null === $plural ? $key.'s' : $plural];