Expose Sources card as something users can input and place in custom layouts

[rebeccaalpert]

IFD has suggested some alternative designs for Sources card navigation. Right now, we do not export the Sources card as a separate piece outside of Messages, so you would have to first create your own and then create a custom layout you could inject into a Message.

It should be a low lift to make the Sources card exportable and use it within Messages.

[rebeccaalpert]

Sources Card with (1 source, 2 sources, etc.) is already exportable - the goal of this is to export just the card as a separate piece.