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

[Matt Arsenault via cfe-commits]

arsenm wrote:

> Actually, even ignoring address space 7, it feels like these builtins if you could `raw.ptr.buffer.store` any type you liked, and then they could be type-varying in Clang?

We could either have a builtin for all the types that would work, or if we want to treat them more like a normal pointer, clang could verify you only use them with types that will work 

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