[clang] [Clang][AMDGPU] Add builtins for instrinsic `llvm.amdgcn.raw.buffer.store` (PR #94576)

[Shilei Tian via cfe-commits]

shiltian wrote:

> maybe add a test for non-constant offset?

Hmm, I thought I added all tests...My bad. Will add it right away.

https://github.com/llvm/llvm-project/pull/94576