[clang] [HLSL] Vector standard conversions (PR #71098)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

Adding some additional reviewers to look over codegen changes and also for another set of eyes on the conversion changes in Sema (the changes look correct to me, but conversion logic is dense enough that getting more eyes on it is a good idea).

https://github.com/llvm/llvm-project/pull/71098