Disambiguate between trashed and permanently deleted Posts and Comments #1260

In develop, a client making a DELETE request to Posts or Comments has no way of distinguishing between whether the request trashed the resource or permanently deleted it. We should provide this detail.

From #1224

Also, 2x DELETE wp/v2/comments/<id> will permanently delete a comment, but 2x DELETE wp/v2/posts/<id> will return some rest_already_deleted error (2d5cf2c, #959). We should make sure these are consistent.