[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]

farzonl wrote:

The `BufferStoreInt64.ll` and `BufferStoreDouble.ll` tests were both updated, but there were no load tests that were updated for these two cases? Is that ok?

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