[clang] [LifetimeSafety] Add multi-block support to buildOriginFlowChain (PR #204592)

[Utkarsh Saxena via cfe-commits]

usx95 wrote:

I will land this for now as I have some upcoming conflicting changes.
@suoyuan666, the pending comments are non-blocking and you can address them in a followup PR.

https://github.com/llvm/llvm-project/pull/204592