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_const_eval/src/util/alignment.rs

@@ -55,7 +55,7 @@ where
             ProjectionElem::Field(..) => {
                 let ty = place_base.ty(local_decls, tcx).ty;
                 match ty.kind() {
-                    ty::Adt(def, _) => return def.repr.pack,
+                    ty::Adt(def, _) => return def.repr().pack,
                     _ => {}
                 }
             }

compiler/rustc_const_eval/src/util/call_kind.rs

@@ -132,7 +132,7 @@ pub fn call_kind<'tcx>(
             .parent(method_did)
             .filter(|did| tcx.def_kind(*did) == rustc_hir::def::DefKind::Impl)
             .and_then(|did| match tcx.type_of(did).kind() {
-                ty::Adt(def, ..) => Some(def.did),
+                ty::Adt(def, ..) => Some(def.did()),
                 _ => None,
             });
         let is_option_or_result = parent_self_ty.map_or(false, |def_id| {