The drop api for collection view seems to be broken in beta 4.
In previous betas the UICollectionViewDropCoordinator had an api to drop into a placeholder that would also create the placeholder:
func drop(_, toPlaceholderInsertedAt:, withReuseIdentifier:)
this api was dropped in beta 11 and instead there is an api:
func drop(_ dragItem: UIDragItem, to placeholder: UICollectionViewDropPlaceholder)
that requires a new class UICollectionViewDropPlaceholder but it's unclear how one would create such an object as it's init requires a reuse identifier and an index path, but get no reference to the collection view where this reuse identifier is registered.
I tried creating such a class thinking maybe the init has access to the active drop session and get a reference to the collection view through that, but the project fails to link yielding an undefined symbol: UICollectionViewDropPlaceholder, meaning this class isn't at all in the uikit framework.
So how is one supposed to do drag and drop in a collection view in beta 4?
