[HLSL] Generate Root Signature Descriptor Table Metadata from AST

[inbelic]

This issue handles the generation of root signature LLVM IR metadata from the parsed AST. Specifically, we will handle this for the DescriptorTable and DescriptorTableClause.

We will again follow the representation of a list of "root elements" following the defined metadata representation.

AC:

• Define CGHLSLRuntime::addRootSignature in CGRuntime.h
• Implement CGHLSLRuntime::addRootSignature in CGRuntime.cpp
• Implement metadata generation for DescriptorTable and DescriptorTableClause in HLSLRootSignatures.[h|cpp]
• Add usage of addRootSignature to emitEntryFunction in CGRuntime.cpp
• Add tests of generated metadata using emit-llvm in CodeGenHLSL/RootSignatures.hlsl

[inbelic]

I have a local patch ready to go but it is blocked for review based on the resolution of: #119011