[clang] [HLSL] Permit template-less HLSL builtin types with default args (PR #216834)

[Diego Novillo via cfe-commits]

https://github.com/dnovillo requested changes to this pull request.

Not really my area, but it looks fine (this is similar to the Texture2D case, right?). Thanks for the tests, but they seem to be failing.

https://github.com/llvm/llvm-project/pull/216834