LibDevTools+LibWebView+WebContent: Selectively fetch DOM node properties

When we inspect a DOM node, we currently serialize many properties for
that node, including its layout, computed style, used fonts, etc. Now
that we aren't piggy-backing on the Inspector interface, we can instead
only serialize the specific information required by DevTools.

Libraries/LibWebView/DOMNodeProperties.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/JsonValue.h>
+#include <LibIPC/Forward.h>
+
+namespace WebView {
+
+struct DOMNodeProperties {
+    enum class Type {
+        ComputedStyle,
+        Layout,
+        UsedFonts,
+    };
+
+    Type type { Type::ComputedStyle };
+    JsonValue properties;
+};
+
+}
+
+namespace IPC {
+
+template<>
+ErrorOr<void> encode(Encoder&, WebView::DOMNodeProperties const&);
+
+template<>
+ErrorOr<WebView::DOMNodeProperties> decode(Decoder&);
+
+}