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

[Oliver Hunt via cfe-commits]

https://github.com/ojhunt approved this pull request.

Yeah, no need for a release note, but @efriedma-quic's request to @llvm-beanz needs to be followed up on 

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