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

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

We should also check whether a loop that simply checks for all whitespaces is faster. All the non-' ' whitespaces are consecutive numbers together, so it boils down to a `(c >= '\t' && c <= '\r') || c == ' '` (though `\n` has special handling, so it might not be as perfect).

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