[clang] [LifetimeSafety] Track origins through nested subobject fields (PR #232867)

[Balázs Benics via cfe-commits]

steakhal wrote:

> LGTM. Please wait for 1-2 other reviewers to make sure I did not miss anything.

My plan was to definitely wait for @usx95 review given that I'm directly depending on his recent patch - and he might have more patches downstream that I could conflict with.

https://github.com/llvm/llvm-project/pull/232867