Support Location Override

[teganscott]

Enable native location override to take incoming user locations and pass it through into mapbox. Trying to override the current experience using layers to mock a blue dot and shifting the camera to follow the blue dot feels inauthentic leading to a poor user experience.

Current limitation

• The Flutter SDK does not expose location.override(provider:) (iOS) or overrideLocationProvider (Android).
• FollowPuckViewportState follows Mapbox's internal GPS provider.

Desired behaviour

• Provide an API to override the location provider in Flutter.
• Allow injecting external location updates (lat, lon, accuracy, heading) from Dart into the overridden provider.
• When overridden, Mapbox GPS should not be active
• FollowPuckViewportState should smoothly follow the injected locations, preserving the current UX.