hir: Simplify hir_owner_nodes query

The query accept arbitrary DefIds, not just owner DefIds.
The return can be an `Option` because if there are no nodes, then it doesn't matter whether it's due to NonOwner or Phantom.
Also rename the query to `opt_hir_owner_nodes`.

compiler/rustc_mir_transform/src/coverage/mod.rs

@@ -452,7 +452,7 @@ fn get_body_span<'tcx>(
 fn hash_mir_source<'tcx>(tcx: TyCtxt<'tcx>, hir_body: &'tcx rustc_hir::Body<'tcx>) -> u64 {
     // FIXME(cjgillot) Stop hashing HIR manually here.
     let owner = hir_body.id().hir_id.owner;
-    tcx.hir_owner_nodes(owner)
+    tcx.opt_hir_owner_nodes(owner)
         .unwrap()
         .opt_hash_including_bodies
         .unwrap()