[HLSL] Add Root Signatures into DX Container

[joaosaffran]

This issue parents the work related to adding root signatures into DX Container using clang.

Upon completed, it is expected we can generate a DX Container blob that contains the Root Signature specification and use a disassembler to inspect DX Container and

As such, this work consists of extracting the root signature from LLVM IR using the specified metadata schema, perform validations to guarantee the data correctness using specified validations, generate a DX Container blob containing the Root Signature definition and we should be able to test the Generated container using a disassembler. Each of these sub-tasks matches to one of the linked sub-issues and so this issue is resolved when all sub-tasks are completed.

For further information on the specification, please refer to this section of the HLSL Root Signature proposal.