Ladybird: Add the node properties tabs to the inspector

This now allows you to view the computed and resolved style values,
along with the CSS variables of a node.

Ladybird/DOMNodeProperties.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2022, MacDue <macdue@dueutil.tech>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+
+namespace Ladybird {
+
+struct DOMNodeProperties {
+    String computed_style_json;
+    String resolved_style_json;
+    String custom_properties_json;
+};
+
+}