* Update C syntax with keywords up to C23.
* Update C syntax with some GCC extensions.
* Update C# syntax with new keywords up to C# 12.
* Update C# syntax with preprocessor directives.
* Add Cake build script (C#) syntax.
* Add MSBuild (XML) syntax.
Use the 'regexp2' library for lookahead and lookbehind in region
start and end regular expressions to support things like closing quotes
that aren't preceded by backslashes.