Support providing multiple drag placeholders

#### Please describe the feature you would like to request.
Currently there is one type of place holder, the one that's defined with the `*cdkDragPlaceholder` directive.
However the destination container might display the `cdkDrag` item different than the original container.

You can see the issue in here:
https://stackblitz.com/edit/angular-terlwz

If you'll try to drag to the done list the place holder there doesn't show the right layout of the component if it would be dropped.

#### What is the use-case or motivation for this proposal?
I need to take item from one container with a certain layout, and drop the element in other container with different layout. since the layout is different and the way the drag item is viewed in the container is different I suppose the place holder also need to be different.

#### Is there anything else we should know?
I'm also using the drag preview for other feature so I can't use it here.
Maybe the container itself should accept a template for rendering an element that is about to be added.

What do you think?

Inizia riproducendo il comportamento dell’esempio StackBlitz collegato e leggendo la direttiva del placeholder di trascinamento e il comportamento del contenitore di destinazione. Il lavoro è completato quando un elemento trascinato può usare un layout del placeholder appropriato per il contenitore in cui sta entrando, senza fare affidamento sull’anteprima di trascinamento esistente.

Scritto dal modello di indicizzazione a partire dal testo della issue.