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/DataCollector/AbstractDataCollector.php

@@ -0,0 +1,35 @@
+<?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\DataCollector;
+
+use Symfony\Component\HttpKernel\DataCollector\DataCollector;
+
+/**
+ * @author Laurent VOULLEMIER <laurent.voullemier@gmail.com>
+ */
+abstract class AbstractDataCollector extends DataCollector implements TemplateAwareDataCollectorInterface
+{
+    public function getName(): string
+    {
+        return static::class;
+    }
+
+    public function reset(): void
+    {
+        $this->data = [];
+    }
+
+    public static function getTemplate(): ?string
+    {
+        return null;
+    }
+}