[clang] [Clang] Track alloca element types to avoid getAllocatedType() calls (PR #181740)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

> > That said this also needs tests
> 
> There isn't really anything to test here, since it is just deleting a use of an API that is about to be deprecated in LLVM (part of the opaque pointer work followups). On net, we'll get to remove a field from every single AllocaInst in exchange for that field being part of DominatingLLVMValue instead when there is a requirement of having a DominatingLLVMValue in use.

I'm not actually sure why I asked for tests? I think I may have added this to the wrong review, I just need to work out where that should have gone

https://github.com/llvm/llvm-project/pull/181740