cs: Add custom PHP CS Fixer configuration.

(cherry picked from commit 54bff1659f5ccdde10e7789998e7899b5bd8e586)

.php-cs-fixer.dist.php

@@ -0,0 +1,21 @@
+<?php
+
+/**
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+use PhpCsFixer\Config;
+
+$config = require __DIR__ . '/vendor/drupol/php-conventions/config/php73/php_cs_fixer.config.php';
+
+/** @var Config $config */
+$config
+    ->getFinder()
+    ->in(
+        [__DIR__ . '/src', __DIR__ . '/tests', __DIR__ . '/tests/benchmarks', __DIR__ . '/tests/static-analysis']
+    );
+
+return $config;

grumphp.yml

@@ -8,6 +8,7 @@ parameters:
 
     # PHP CS Fixer
     tasks.phpcsfixer.diff: true
+    tasks.phpcsfixer.config: .php-cs-fixer.dist.php
 
     # PHPCS
     tasks.phpcs.ignore_patterns: