[llvm] [DirectX backend] emits metadata for DXIL version. (PR #88350)

[Justin Bogner via llvm-commits]

bogner wrote:

I think we should probably just do the simpler `dxil::createDXILVersionMD` version of this for now, rather than adding the DXILVersion abstraction. The DXILVersion abstraction is similar to the prototype shader model abstraction in #66015, but having thought about what I was doing there for a bit I think it's overengineered and won't scale very well to the rest of the stuff we store in metadata.

Longer term I'd like to go the route of #63835, where we introduce a metadata analysis pass that generates some kind of `DXILMetadata` type that can abstract over the metadata stuff a bit more simply.

https://github.com/llvm/llvm-project/pull/88350