Auto merge of #38897 - nikomatsakis:issue-32330-followup, r=arielb1

make lifetimes that only appear in return type early-bound

This is the full and proper fix for #32330. This also makes some effort to give a nice error message (as evidenced by the `ui` test), sending users over to the tracking issue for a fuller explanation and offering a `--explain` message in some cases.

This needs a crater run before we land.

r? @arielb1