[clang] [HLSL][RootSignature] Implement Lexing of DescriptorTables (PR #122981)

[Chris B via cfe-commits]

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

My last real question here is whether this belongs in clang/Parse or if it should be in clang/Lex. Since it is now strictly Lexing it shouldn't have any dependencies on the parse or AST libraries right?

https://github.com/llvm/llvm-project/pull/122981