Rollup merge of #72508 - ecstatic-morse:poly-self-ty, r=nikomatsakis

Make `PolyTraitRef::self_ty` return `Binder<Ty>`

This came up during review of #71618. The current implementation is the same as a call to `skip_binder` but harder to audit. Make it preserve binding levels and add a call to `skip_binder` at all use sites so they can be audited as part of #72507.

clippy_lints/src/future_not_send.rs

@@ -95,7 +95,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FutureNotSend {
                                         let trait_ref = trait_pred.to_poly_trait_ref();
                                         db.note(&*format!(
                                             "`{}` doesn't implement `{}`",
-                                            trait_ref.self_ty(),
+                                            trait_ref.skip_binder().self_ty(),
                                             trait_ref.print_only_trait_path(),
                                         ));
                                     }