Create the API

Closes #3464692

core/lib/Drupal/Core/Config/Entity/ComparatorBase.php

+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Core\Config\Entity;
+
+class ComparatorBase implements ComparatorInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEquivalent(array $a, array $b): bool {
+    // Ensure we don't get a false mismatch due to differing key order.
+    // @todo When https://www.drupal.org/project/drupal/issues/3230826 is
+    //   fixed in core, use that API instead to sort the config data.
+    static::recursiveSortByKey($a);
+    static::recursiveSortByKey($b);
+
+    return $a == $b;
+  }
+
+  protected static function recursiveSortByKey(array &$data): void {
+    // If the array is a list, it is by definition already sorted.
+    if (!array_is_list($data)) {
+      ksort($data);
+    }
+    foreach ($data as &$value) {
+      if (is_array($value)) {
+        static::recursiveSortByKey($value);
+      }
+    }
+  }
+
+}