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/framework-bundle/CacheWarmer/CachePoolClearerCacheWarmer.php

@@ -0,0 +1,64 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Bundle\FrameworkBundle\CacheWarmer;
+
+use Symfony\Component\HttpKernel\CacheClearer\Psr6CacheClearer;
+use Symfony\Component\HttpKernel\CacheWarmer\CacheWarmerInterface;
+
+/**
+ * Clears the cache pools when warming up the cache.
+ *
+ * Do not use in production!
+ *
+ * @author Teoh Han Hui <teohhanhui@gmail.com>
+ *
+ * @internal
+ */
+final class CachePoolClearerCacheWarmer implements CacheWarmerInterface
+{
+    private $poolClearer;
+    private $pools;
+
+    /**
+     * @param string[] $pools
+     */
+    public function __construct(Psr6CacheClearer $poolClearer, array $pools = [])
+    {
+        $this->poolClearer = $poolClearer;
+        $this->pools = $pools;
+    }
+
+    /**
+     * {@inheritdoc}
+     *
+     * @return string[]
+     */
+    public function warmUp(string $cacheDirectory): array
+    {
+        foreach ($this->pools as $pool) {
+            if ($this->poolClearer->hasPool($pool)) {
+                $this->poolClearer->clearPool($pool);
+            }
+        }
+
+        return [];
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isOptional(): bool
+    {
+        // optional cache warmers are not run when handling the request
+        return false;
+    }
+}