Update Select Feature Example to Use Expressions

[riastrad]

The iOS feature selection example relies on expressions, but currently the Android equivalent does not leverage this.

I think this might be a good opportunity to refactor the SelectBuildingActivity to show off the Power of Expressions™.

My current thinking is that this change would be as simple as updating the onMapClick function to do this:

fillLayer.setProperties(
     opacity(
         match("<feature-name>",
             "<selected-feature-name>", 1,
             0
         );
     )
 );

(Instead of generating and re-drawing a new polygon on every map tap.)