[llvm] [llvm] Ensure propagated constants in the vtable are aligned (PR #136630)

[via llvm-commits]

PiJoules wrote:

> I see some new tests. Can we get those precommited, so it's easy to understand the full delta of your compiler change?

You're referring to having a PR with just `virtual-const-prop-small-alignment-32/64.ll` without the functional changes in this PR?

https://github.com/llvm/llvm-project/pull/136630