[clang] [llvm] [HLSL] Add ConstantBuffer<T> (PR #195153)

[Steven Perron via cfe-commits]

s-perron wrote:

@hekota I've updated the tests to work with your change. Let me know when #194989 is merged, and then I'll rebase and merge.

https://github.com/llvm/llvm-project/pull/195153