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/HttpCache/StoreInterface.php

@@ -27,7 +27,7 @@ interface StoreInterface
     /**
      * Locates a cached Response for the Request provided.
      *
-     * @return Response|null A Response instance, or null if no cache entry was found
+     * @return Response|null
      */
     public function lookup(Request $request);
 
@@ -70,11 +70,9 @@ interface StoreInterface
     /**
      * Purges data for the given URL.
      *
-     * @param string $url A URL
-     *
      * @return bool true if the URL exists and has been purged, false otherwise
      */
-    public function purge($url);
+    public function purge(string $url);
 
     /**
      * Cleanups storage.