Update heading orientation when device orientation changes

[1ec5]

When the device’s orientation changes between portrait and landscape, we need to update any CLLocationManager’s headingOrientation property to reflect the new device orientation. Otherwise, headings (and course readings?) may be off by up to 90°. The map SDK updates its location manager’s heading orientation whenever -layoutSubviews gets called on MGLMapView, since the view hierarchy is always updated on orientation changes. But this library can observe UIDeviceOrientationDidChangeNotification.

/ref mapbox/mapbox-navigation-ios#1942 (comment)
/cc @rclee

[1ec5]

I momentarily forgot that course is independent of the device’s heading and therefore independent of its orientation too. Meanwhile, this library doesn’t record the heading at all, so we’re good here.

[rclee]

We're not collecting course at the moment either. 😄 https://github.com/mapbox/mobile-telemetry/issues/19