[llvm] [HLSL][RootSignature] Implement serialized dump of Descriptor Tables (PR #138326)

[Finn Plummer via llvm-commits]

inbelic wrote:

The data structures are only constructed through using the `RootSignatureParser`, so they will have been had basic validation (enums/flags will be valid). I don't think that we should be concerned with handling invalid data-values.

https://github.com/llvm/llvm-project/pull/138326