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

[Utkarsh Saxena via cfe-commits]

usx95 wrote:

Debug output could be helpful to debug stuff when things went wrong; but to explain how the code is working, I would rely on improving the documentation of both the overloads of `buildOriginFlowChain`. Currently they do not include any documentation for the steps involved.

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