[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:

> > We need a typedbuffer test cases that has two runlines. One where we specify in the target flag sm6.2 and one where we specify sm6.3. This way we have a case where we show the backport support and the difference of behaviors between the two shader models.
> 
> If you meant to test that RawBuffer Load and Store work in SM6.3 and later; there are existing tests in RawBufferStore.ll and RawBufferLoad.ll

Not exactly We have some work we need to do to document all the backporting work 
https://github.com/llvm/llvm-project/issues/123812

So what I'd like to do is have test cases with seperate runlines for the different shader models for all the cases where we are making active decisions to be different based on shader model like this PR is doing.

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