Rollup merge of #95731 - oli-obk:lazy_tait_regression, r=compiler-errors

Check that all hidden types are the same and then deduplicate them.

fixes #95538

This used to trigger a sanity check. Now we accept that there may be multiple places where a hidden type is constrained and we merge all of these at the end.

Ideally we'd merge eagerly, but that is a larger refactoring that I don't want to put into a backport