[HLSL][RootSignature] Implement initial parsing of the descriptor table clause params (#133800)

- Defines `ParseDescriptorTableClauseParams` to establish the pattern of
how we will parse parameters in root signatures. Namely, to use
recursive descent parsing in a way that follows closely to the EBNF
notation definition in the root signature spec.

- Implements parsing of two param types: `UInt32` and `Register` to
demonstrate the parsing implementation and allow for unit testing

- Changes the calling convention to use `std::optional` return values
instead of boolean error returns and parameters by reference

Part two of implementing:
https://github.com/llvm/llvm-project/issues/126569

---------

Co-authored-by: Finn Plummer <finnplummer@microsoft.com>

0 files changed, 0 insertions, 0 deletions