Add road name to iOS and Android default display

[ianthetechie]

Most navigation apps can show you the current road name at the bottom of the screen (usually just above your ETA). We should support the same.

In order to support this, we should add the current road name to the view model / observed object. Every routing API that I'm familiar with (Valhalla, OSRM, GraphHopper, and Mapbox Directions) includes this information in route responses by default, so I think we can just make this an optional string on both the view models and RouteStep.

Related issues:

• [iOS] Current road name composable UI (Portrait) #244
• [Android] Current road name composable UI (portrait orientation) #245
• [Android] Current road name composable UI (landscape orientation) #308
• [iOS] Current road name composable UI (Landscape) #309