HTML API: Prevent Open Elements class from waking up.

This class accepts a Closure, but it should not be possible
to wake up with one from a serialized class instance.

Developed in https://github.com/WordPress/wordpress-develop/pull/6852
Discussed in https://core.trac.wordpress.org/ticket/61348

Props jonsurrell.
See #61348.
Follow-up to [58304].

Built from https://develop.svn.wordpress.org/trunk@58441


git-svn-id: http://core.svn.wordpress.org/trunk@57890 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/html-api/class-wp-html-open-elements.php

@@ -517,4 +517,13 @@ class WP_HTML_Open_Elements {
 			( $this->pop_handler )( $item );
 		}
 	}
+
+	/**
+	 * Wakeup magic method.
+	 *
+	 * @since 6.6.0
+	 */
+	public function __wakeup() {
+		throw new \LogicException( __CLASS__ . ' should never be unserialized' );
+	}
 }