Bespoke course tracking

[1ec5]

This issue tracks implementing turn-by-turn-specific course tracking behavior within NavigationMapView instead of relying on the course tracking built into the map SDK. That would allow us to:

• More cleanly expose user puck customization to the developer (Can't change user's current location annotation view #213)
• Clean up or simulate location updates without the redeclaration hack and without interference from the map SDK (Allow updating location puck bottom offset #323, Navigation not working when app going to background and back to foreground. #341)
• More precisely customize the on-screen location of the user puck (Allow overriding the location puck's location #324)
• Continue to display a puck instead of a dot as the user pans away

To be sure, each of those issues is surmountable on its own, but taken together, they add up to code that’s unintuitive and fragile. The map SDK’s built-in course tracking is actually not that complicated. What’s complicated are the transitions to other user tracking modes, but we might want custom behavior for that anyways.

/cc @frederoni @bsudekum @ericrwolfe @boundsj

[1ec5]

The cruxt of the map SDK’s implementation is in:

• -directionByFollowingWithCourse, which we essentially override already
• -edgePaddingForFollowingWithCourse, which we want to customize anyways
• https://github.com/mapbox/mapbox-gl-native/blob/05df451f3c370e6ba8a02d8b0268d88c23db269b/platform/ios/src/MGLMapView.mm#L4532-L4547

There are a few other parts of the code that deal with:

• transitions in and out of course tracking mode (which we don’t really need)
• targeted course tracking mode (which we don’t use; this library has its own overview logic)
• flying to distant location updates, such as after leaving a tunnel, although this behavior is controversial: reduce flyTo time for large distances mapbox-gl-native#5794

[1ec5]

In this first pass – at least until we have design resources – we’d need to port over the parts of MGLFaux3DUserLocationAnnotationView that pertain to the user puck (as opposed to the user dot).