[clang] [HLSL] Finish exposing half types and intrinsics always (PR #132804)

[Sarah Spall via cfe-commits]

spall wrote:

> For example, for `abs`, it still depends on the _HLSL_16BIT_AVAILABILITY availability attribute. Does this PR intend to keep abs overloads using half "unexposed"? Or should that overload for abs be exposed too?

I'm not sure I understand the question, I think abs is the same as the ones in this PR are modified to be. 

https://github.com/llvm/llvm-project/pull/132804