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/cache/Adapter/AdapterInterface.php

@@ -14,6 +14,9 @@ namespace Symfony\Component\Cache\Adapter;
 use Psr\Cache\CacheItemPoolInterface;
 use Symfony\Component\Cache\CacheItem;
 
+// Help opcache.preload discover always-needed symbols
+class_exists(CacheItem::class);
+
 /**
  * Interface for adapters managing instances of Symfony's CacheItem.
  *
@@ -31,7 +34,14 @@ interface AdapterInterface extends CacheItemPoolInterface
     /**
      * {@inheritdoc}
      *
-     * @return \Traversable|CacheItem[]
+     * @return \Traversable<string, CacheItem>
      */
     public function getItems(array $keys = []);
+
+    /**
+     * {@inheritdoc}
+     *
+     * @return bool
+     */
+    public function clear(string $prefix = '');
 }