[llvm] [DirectX] Add support for Raw Buffer Loads and Stores for scalars and vectors of doubles and i64s in SM6.2 and earlier (PR #146627)

[Farzon Lotfi via llvm-commits]

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

Code looks good.  We should probably discuss how to test and document cases where we change behavior based on shader model since it is something we will need to work on in the near future.

https://github.com/llvm/llvm-project/pull/146627