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

[Joshua Batista via cfe-commits]

bob80905 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?
> 
> Oh I see what you are referring to. That might be my mistake; let me double check if I used the wrong __HLSL_AVAILABILITY

Yeah, if the intention of this PR is to expose all half type overloads always, then I would think there is no more utility in defining
`HLSL_16BIT_AVAILABILITY` anymore.

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