[clang] Fix implicit truncation of `select` non-bool vector conditions (PR #166279)

[Kaitlin Peng via cfe-commits]

kmpeng wrote:

If you mean just using `HLSL_FIXED_VECTOR` and not separating the templates, I think we would end up running into the same template deduction problem. 

https://github.com/llvm/llvm-project/pull/166279