Stable type identifiers: a missing piece for crABI and export

Yes, I was incorrect about what I thought #3435 needed. My proposed solution addresses a different problem than what #3435 was originally intended for; specifically, stable type identification of a type across different compiler versions/builds, not detecting an ABI incompatible change. There are two different problems. Is there any existing work or discussion on stable type identification that is not tied directly to ABI compatibility?