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/RebootableInterface.php

@@ -21,10 +21,10 @@ interface RebootableInterface
     /**
      * Reboots a kernel.
      *
-     * The getCacheDir() method of a rebootable kernel should not be called
-     * while building the container. Use the %kernel.cache_dir% parameter instead.
+     * The getBuildDir() method of a rebootable kernel should not be called
+     * while building the container. Use the %kernel.build_dir% parameter instead.
      *
-     * @param string|null $warmupDir pass null to reboot in the regular cache directory
+     * @param string|null $warmupDir pass null to reboot in the regular build directory
      */
-    public function reboot($warmupDir);
+    public function reboot(?string $warmupDir);
 }