Introduce TwigFileSystemCache

The original FileSystemCache of twig generates the key depending on PHP_VERSION.
We need to produce the same key regardless of PHP_VERSION. Therefore
TwigFileSystemCache overwrites this method.

[MAILPOET-3985]

mailpoet/lib/Config/TwigFileSystemCache.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace MailPoet\Config;
+
+class TwigFileSystemCache extends \MailPoetVendor\Twig\Cache\FilesystemCache {
+
+  private $directory;
+
+  public function __construct(
+    string $directory,
+    int $options = 0
+  ) {
+    $this->directory = \rtrim($directory, '\\/') . '/';
+    parent::__construct($directory, $options);
+  }
+
+  public function generateKey(string $name, string $className): string {
+    $hash = \hash('sha256', $className);
+    return $this->directory . $hash[0] . $hash[1] . '/' . $hash . '.php';
+  }
+}