[llvm] [DirectX] Updating DXContainer Yaml to represent Root Signature 1.2 (PR #159659)

[Justin Bogner via llvm-commits]

https://github.com/bogner approved this pull request.

Looks good once @inbelic's comments are addressed, and one comment about a strange looking choice.

https://github.com/llvm/llvm-project/pull/159659