Return (-1, -1) if point for coordinate is out of map's bounds

[maios]

Fixes MAPSIOS-252
In MapboxMap.point(for:) if the coordinate is outside of map view's bounds it will return (-1, -1), however, when using MapboxMap.points(for:) it will return an actual coordinate. Based on @endanke's comment we should update MapboxMap.points(for) to also return (-1, -1) for coordinate that is outside of map view's bounds.

Pull request checklist:

• Write tests for all new functionality. If tests were not written, please explain why.
• Add documentation comments for any added or updated public APIs.
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