[clang] [Clang][Lexer][Performance] Optimize Lexer whitespace skipping logic (PR #180819)

[Nikolas Klauser via cfe-commits]

https://github.com/philnik777 commented:

Would it make more sense to avoid the table lookup maybe? Simply checking for the few possible values can be really efficient: https://godbolt.org/z/Ef8cbKnvr

https://github.com/llvm/llvm-project/pull/180819