Rollup merge of #117241 - compiler-errors:auto-trait-leak-cycle, r=oli-obk

Stash and cancel cycle errors for auto trait leakage in opaques

We don't need to emit a traditional cycle error when we have a selection error that explains what's going on but in more detail.

We may want to augment this error to actually point out the cycle, now that the cycle error is not being emitted. We could do that by storing the set of opaques that was in the `CyclePlaceholder` that gets returned from `type_of_opaque`.

r? `@oli-obk` cc `@estebank` #117235

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -3104,6 +3104,13 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 );
             }
         };
+
+        if let Some(diag) =
+            self.tcx.sess.diagnostic().steal_diagnostic(self.tcx.def_span(def_id), StashKey::Cycle)
+        {
+            diag.cancel();
+        }
+
         err
     }