[DirectX] Setup root signature DXIL Lowering.

[joaosaffran]

This issue focus on setting up the LLVM related code to support the extraction of root signatures from LLVM IR metadata and lowering it to DX Container binary format.

AC:

• Add a Root Signature analysis pass to extract root signature metadata from LLVM IR.
• Add validation stage to check extracted data.
• Add the analysis into DirectX backend.
• Add the analysis into DXContainerGlobals dependencies.
• Add test to check the generated data and validations are executed correctly.