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/Resource/SelfCheckingResourceChecker.php

@@ -23,14 +23,24 @@ use Symfony\Component\Config\ResourceCheckerInterface;
  */
 class SelfCheckingResourceChecker implements ResourceCheckerInterface
 {
+    // Common shared cache, because this checker can be used in different
+    // situations. For example, when using the full stack framework, the router
+    // and the container have their own cache. But they may check the very same
+    // resources
+    private static $cache = [];
+
     public function supports(ResourceInterface $metadata)
     {
         return $metadata instanceof SelfCheckingResourceInterface;
     }
 
-    public function isFresh(ResourceInterface $resource, $timestamp)
+    /**
+     * @param SelfCheckingResourceInterface $resource
+     */
+    public function isFresh(ResourceInterface $resource, int $timestamp)
     {
-        /* @var SelfCheckingResourceInterface $resource */
-        return $resource->isFresh($timestamp);
+        $key = "$resource:$timestamp";
+
+        return self::$cache[$key] ?? self::$cache[$key] = $resource->isFresh($timestamp);
     }
 }