[clang] [LifetimeSafety] Implement multi-level origins (PR #168344)

[Yitzhak Mandelbaum via cfe-commits]

ymand wrote:

> 4. **Multi-Level Flow Propagation**: The `flow` function propagates origins through all depths of the lists with a critical assertion:
>    `assert(Dst->getDepth() == Src->getDepth() && "Lists must have the same length");` This ensures type safety in origin propagation during expression handling. (Rant with relief: This `assert`​ was quite hard to get right but it helped make the right changes).

rant acknowledged. :) Sounds like struggling to get an induction hypothesis correct :)

https://github.com/llvm/llvm-project/pull/168344