Some syntax highlighting updates for C and C#.

[alexrp]

• Update keywords for C23 and add some extension keywords.
• Update keywords for C# 12 and add preprocessor directives.
• Add syntax for Cake build scripts (based on C#).
• Add syntax for various MSBuild files (just plain old XML).

[JoeKar]

We're happy about every one who is willing to help here and trying to maintain something. :)