Fix implied outlives check for GAT in RPITIT We enforce certain `Self: 'lt` bounds for GATs to save space for more sophisticated implied bounds, but those currently operate on the HIR. Code was easily reworked to operate on def-ids so that we can properly let these suggestions propagate through synthetic associated types like RPITITs and AFITs. r? `@jackh726` or `@aliemjay` Fixes #116789