don't ice on non-lifetime binders under -Zassumptions-on-binders

[Dnreikronos]

fixes #157778

w/ -Znext-solver=globally -Zassumptions-on-binders and a non-lifetime binder we hit assert!(max_universe < u) in pull_region_outlives_constraints_out_of_universe and ICE.

the machinery here is region-outlives only, but a for<T> binder leaves a placeholder type in universe u that the region-only rewrite can't pull out, so an alias outlives like <!T as Trait>::Assoc: 'r reaches that assert still in u. just report ambiguity in that case, same as the None => Ambiguity bails right next to it — now it errors normally (E0284) instead of ICEing.

r? @lcnr

[lcnr]

r? BoxyUwU

[BoxyUwU]

can you move this logic into rewrite_type_outlives_constraints_in_universe_for_eager_placeholder_handling 🤔 it feels surprising that pull_region_outlives_constraints would do anything to type outlives constraints and similarly that rewrite_type_outlives_constraints wouldn't fully handle type outlives' :3

[Dnreikronos]

done, moved this into rewrite_type_outlives_constraints_in_universe_for_eager_placeholder_handling.

pull_region_outlives_constraints_out_of_universe is back to just asserting that any ty-outlives constraint it sees was already moved below u. the alias rewrite handles the leftover non-lifetime placeholder case now, and turns it into ambiguity before the region-only pass runs.

idk if this is the exact shape you had in mind, but lgtm locally. imp bit is that pull_region_outlives_constraints_out_of_universe doesn't decide ty-outlives stuff anymore.