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/CMakeLists.txt

@@ -4,6 +4,7 @@ set(SOURCES
     DOMTreeModel.cpp
     OutOfProcessWebView.cpp
     RequestServerAdapter.cpp
+    SourceHighlighter.cpp
     StylePropertiesModel.cpp
     ViewImplementation.cpp
     WebContentClient.cpp