[clang] [clang][dataflow] Add synthetic fields to `RecordStorageLocation` (PR #73860)

[Yitzhak Mandelbaum via cfe-commits]

https://github.com/ymand approved this pull request.

This is amazing! I spent a while searching for changes to join/widen to account for synthetic fields and then realized that (of course!) no special handling is needed!

I also love that we now have the hooks we've wanted since the beginning.

Thank you!

https://github.com/llvm/llvm-project/pull/73860