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

[Chris B via cfe-commits]

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llvm-beanz wrote:

As I said in your other PR, I believe not including error reporting and the appropriate testing makes it significantly more difficult to review the subsequent commit since not all the appropriate code will even be in the PR.

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