Improve AdtDef interning.

This commit makes `AdtDef` use `Interned`. Much the commit is tedious
changes to introduce getter functions. The interesting changes are in
`compiler/rustc_middle/src/ty/adt.rs`.

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -676,7 +676,7 @@ fn fundamental_ty_inner_tys<'tcx>(
             match types.next() {
                 None => {
                     tcx.sess.span_err(
-                        tcx.def_span(def.did),
+                        tcx.def_span(def.did()),
                         "`#[fundamental]` requires at least one type parameter",
                     );
 
@@ -729,7 +729,7 @@ fn ty_is_local_constructor(ty: Ty<'_>, in_crate: InCrate) -> bool {
             InCrate::Remote => true,
         },
 
-        ty::Adt(def, _) => def_id_is_local(def.did, in_crate),
+        ty::Adt(def, _) => def_id_is_local(def.did(), in_crate),
         ty::Foreign(did) => def_id_is_local(did, in_crate),
         ty::Opaque(..) => {
             // This merits some explanation.