iOS: New Reference Asset - Choice

[hborawski]

Depends on #181

Consuming the new core choice, provide a rendering implementation in SwiftUI that displays the asset a list of "tiles". While the React implementation will use radio buttons, that UX is not as ideal on mobile devices, and we should opt for slightly larger controls.

A "tile" can be described as follows:

• A tile is a container with rounded corners, and a slight shadow to lift it off the content behind it
• A tile that is currently selected has no shadow, and a green stroke around the border of the tile

For this choice asset:

• Render the label of each choice entry inside each tile

• Render the title of the choice above the list of tiles

• Render validation information below the list of tiles

[GauravKesarwani]

@mercillo @hborawski Can I work on this issue ?