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

[Jameson Nash via cfe-commits]

vtjnash 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.

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