feat: Add Htmlable contract interface for HTTP responses (#6794)

Author: huangdijia

src/Htmlable.php

@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * This file is part of Hyperf.
+ *
+ * @link     https://www.hyperf.io
+ * @document https://hyperf.wiki
+ * @contact  [email protected]
+ * @license  https://github.com/hyperf/hyperf/blob/master/LICENSE
+ */
+
+namespace Hyperf\Contract;
+
+use Stringable;
+
+interface Htmlable extends Stringable
+{
+    /**
+     * Get content as a string of HTML.
+     *
+     * @return string
+     */
+    public function toHtml();
+}