Please add _onDropItem to ActorSheet class

ActorSheet contains a method _onDropItem. It is private, so it's technically not part of the API. However, I need to override and call it from my actor sheet. What do you think about adding it to the type definitions even though it's documented to be private? It would be a great help. The type would be

  _onDropItem(event: DragEvent, data: object): Promise<unknown>;

Theoretically, we could use a more concrete type for the return type but it's relatively complicated. Personally I don't need it. It is also pretty irrelevant because you're probably not going to call that method yourself and I'm not even sure if the return type is really used anywhere.