[clang] [HLSL] Implement the SV_InstanceID semantic (PR #221091)

[Jonathan Zakharov via cfe-commits]

jzakharovnv wrote:

> > Found a bug when adding more testing, per @inbelic! Please take another look when you can. Thanks!
> 
> Sorry, not sure where should I be looking?

Oops, I pushed my OTS changes but forgot to push on Clang. In my latest OTS commit I added a test case which uncovered a bug with my implementation of `SV_InstanceID`. I initially forgot handle differences in base offset conventions between VK and DX.

Let me go about making a new PR though, its just a small change.

https://github.com/llvm/llvm-project/pull/221091