[HLSL] Construct Root Signature data structures from LLVM IR metadata

[joaosaffran]

This issue handles the construction of low level Root Signature data structures from the LLVM IR metadata.

This issue will focus on extracting the LLVM IR Root Signature related metadata, the validations will defer to this issue: #121491,

AC:

• Define DXContainerRootSignature data structures, using reference implementation from DXC.
• Define and implement RootSignatureMDExtractor during DXContainer code generation.
• Add unit testing of generated data structures.

Here is a list of Root elements to add support to:

• RootFlags - [DXIL] Add support for root signature flag element in DXContainer #123147
• RootConstants - [DXIL] Add support for root signature Constants element Generation in DXContainer  #124967
• RootCBV
• RootSRV
• RootUAV
• DescriptorTable
• StaticSampler