[clang] [LifetimeSafety] Track origins for lifetimebound calls returning record types (PR #187917)

[Utkarsh Saxena via cfe-commits]

usx95 wrote:

> Reference-returning lifetimebound function copied into value: not tracked

This should not just be fine but also required in practice. Consider:   
`const std::string& max(const std::string&& [[lb]], const std::string& [[lb]])`

It is fine to have a copy of the returned reference, and the reference only has the lifetime constraints.

https://github.com/llvm/llvm-project/pull/187917