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/dependency-injection/Config/ContainerParametersResource.php

@@ -17,8 +17,10 @@ use Symfony\Component\Config\Resource\ResourceInterface;
  * Tracks container parameters.
  *
  * @author Maxime Steinhausser <maxime.steinhausser@gmail.com>
+ *
+ * @final
  */
-class ContainerParametersResource implements ResourceInterface, \Serializable
+class ContainerParametersResource implements ResourceInterface
 {
     private $parameters;
 
@@ -30,34 +32,12 @@ class ContainerParametersResource implements ResourceInterface, \Serializable
         $this->parameters = $parameters;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function __toString()
+    public function __toString(): string
     {
         return 'container_parameters_'.md5(serialize($this->parameters));
     }
 
-    /**
-     * @internal
-     */
-    public function serialize()
-    {
-        return serialize($this->parameters);
-    }
-
-    /**
-     * @internal
-     */
-    public function unserialize($serialized)
-    {
-        $this->parameters = unserialize($serialized);
-    }
-
-    /**
-     * @return array Tracked parameters
-     */
-    public function getParameters()
+    public function getParameters(): array
     {
         return $this->parameters;
     }