Implement Suspend/Resume on iOS MapView

[xivk]

Implement a suspend/resume option on the iOS MapView to suspend rendering:

bool _renderingSuspended = false;

public void Pause()
{
    Map.Pause();
    _renderingSuspended = true;
}

public void Resume()
{
    _renderingSuspended = false;
    Map.Resume();
    Render();
}