[clang] [HLSL] standardize builtin unit tests (PR #83340)

[Farzon Lotfi via cfe-commits]

farzonl wrote:

> Do we have the suggestions that this is responding to written down somewhere? I think it would be useful to have those guidelines for anyone who might want to contribute HLSL tests. At any rate, I'd like to know the ones that this is in response to.
@pow2clk 
below are the three comments that inspired this pr:
https://github.com/llvm/llvm-project/pull/83315#discussion_r1506485695
https://github.com/llvm/llvm-project/pull/81190#discussion_r1491951377
https://github.com/llvm/llvm-project/pull/82827#discussion_r1501220875

These were on the fly comments so we don't have  guidelines yet, but that could be something nice to add. I'll talk to @bogner  and find out where to add that.



https://github.com/llvm/llvm-project/pull/83340