Fix use of bare trait objects everywhere

compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs

@@ -62,7 +62,7 @@ fn scrape_region_constraints<'tcx, R>(
     infcx: &InferCtxt<'_, 'tcx>,
     op: impl FnOnce() -> Fallible<InferOk<'tcx, R>>,
 ) -> Fallible<(R, Option<Rc<QueryRegionConstraints<'tcx>>>)> {
-    let mut fulfill_cx = TraitEngine::new(infcx.tcx);
+    let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
     let dummy_body_id = ObligationCause::dummy().body_id;
 
     // During NLL, we expect that nobody will register region