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

[Damyan Pepper via cfe-commits]

https://github.com/damyanp commented:

LGTM - I'm surprised we don't have all of the tokens we're going to need for root signatures included in this PR.

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