Fix impl Trait Lifetime Handling

After this change, impl Trait existentials are
desugared to a new `abstract type` definition
paired with a set of lifetimes to apply.

In-scope generics are included as parents of the
`abstract type` generics. Parent regions are
replaced with static, and parent regions
referenced in the `impl Trait` type are duplicated
at the end of the `abstract type`'s generics.

src/librustdoc/clean/mod.rs

@@ -1960,9 +1960,8 @@ impl Clean<Type> for hir::Ty {
                 }
             }
             TyBareFn(ref barefn) => BareFunction(box barefn.clean(cx)),
-            TyImplTraitExistential(ref bounds) |
-                TyImplTraitUniversal(_, ref bounds) =>
-                    ImplTrait(bounds.clean(cx)),
+            TyImplTraitExistential(ref exist_ty, ref _lts) => ImplTrait(exist_ty.bounds.clean(cx)),
+            TyImplTraitUniversal(_, ref bounds) => ImplTrait(bounds.clean(cx)),
             TyInfer | TyErr => Infer,
             TyTypeof(..) => panic!("Unimplemented type {:?}", self.node),
         }