[clang] [llvm] [HLSL][RootSignature] Implement parsing of `RootFlags` (PR #121799)

[Chris B via llvm-commits]

https://github.com/llvm-beanz commented:

Is there a reason that you're just operating on a StringRef buffer instead of building out a proper tokenizer and parser? It seems to me like root signature parsing probably warrants full lexer and parser that operates on tokens rather than just sections of the substring.

https://github.com/llvm/llvm-project/pull/121799