[llvm] [DirectX] Adding support for Root Descriptors in obj2yaml/yaml2obj (PR #137259)

[Justin Bogner via llvm-commits]

https://github.com/bogner commented:

Some of the encapsulation between the Object and MC layer here feel a bit awkward, but I think it makes sense to hold off on that feedback as the upcoming #137284 makes some pretty significant changes and it'll be easier to discuss there.

A couple of changes requested below.

https://github.com/llvm/llvm-project/pull/137259