refactor: use subclasses for different actor types

src/actor/creature/creature.ts

@@ -0,0 +1,17 @@
+// SPDX-FileCopyrightText: 2022 Johannes Loher
+//
+// SPDX-License-Identifier: MIT
+
+import { ItemType } from "../../item/item-data-source";
+import { DS4Actor } from "../actor";
+
+export class DS4Creature extends DS4Actor {
+    /** @override */
+    get ownableItemTypes(): Array<ItemType> {
+        return [...super.ownableItemTypes, "specialCreatureAbility"];
+    }
+}
+
+export interface DS4Creature {
+    data: foundry.data.ActorData & { type: "creature"; _source: { type: "creature" } };
+}