Expose `DefId::is_local`

We are currently missing [`DefId::is_local`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/def_id/struct.DefId.html#method.is_local); we have the [`Crate.is_local`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_public/struct.Crate.html#structfield.is_local) field but it's not public and I'm not sure how to do `DefId → Crate` 