LibWebView: Create a method to syntax-highlight page source with HTML

This tokenizes a page's source to produce HTML with syntax highlighting.
The first implementation here is rather simple; we do not yet implement
code folding, line numbers, etc.

The goal is for this to be used as the View Source implementation for
all Ladybird chromes.

Userland/Libraries/LibWebView/SourceHighlighter.h

@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <AK/StringView.h>
+
+namespace WebView {
+
+String highlight_source(URL const&, StringView);
+
+}