LibWeb: Implement first draft of CSS syntax highlighting :^)

This works at the Token level, which is quick and easy but has
drawbacks: We don't know when something is a property name or a value,
or if something is part of a selector. But, this works for now.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -49,6 +49,7 @@ set(SOURCES
     CSS/StyleSheetList.cpp
     CSS/StyleValue.cpp
     CSS/Supports.cpp
+    CSS/SyntaxHighlighter/SyntaxHighlighter.cpp
     CSS/ValueID.cpp
     CSS/ValueID.h
     Cookie/ParsedCookie.cpp