Expose MapView#setOfflineRegion

[tobrun]

A common issue that developers run into when integrating offline, is that a specific map configuration is needed to get their offline region loaded correctly (an example of misconfiguration here. To make this easier, we could expose MapView#setOfflineRegion that would take in a offline region definition and load the related style and position the camera automatically.

[LukasPaczos]

Clarifying, the main issue is that when there is no internet connection the onMapReady callback doesn't fire, because default mapbox style failed to load, and users can't load their downloaded offline region that is using a custom style. They'd have to declare that custom style upfront with MapboxMapOptions or via xml which causes a lot of confusion.

We need to document this phenomenon extensively and introducing a method like MapView#setInitialOfflineRegion might bring attention that an action needs to be taken in order to initially load an offline region.