Rollup merge of rust-lang#102829 - compiler-errors:rename-impl-item-kind, r=TaKO8Ki

rename `ImplItemKind::TyAlias` to `ImplItemKind::Type`

The naming of this variant seems inconsistent given that this is not really a "type alias", and the associated type variant for `TraitItemKind` is just called `Type`.

Author: JohnTitor