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

[Joshua Batista via cfe-commits]

https://github.com/bob80905 commented:

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?

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