Allow the application to curate and customize floating map buttons

[1ec5]

We’ve had a number of requests over the years to make the floating map buttons more configurable – to remove a button (#2102), add a button, change the look of a button (#2103), move the buttons to the other side of NavigationViewController, lay them out horizontally (#1139), and so on. It’s already possible to remove the feedback button by setting NavigationViewController.showsReportFeedback, but the other buttons are hard-coded.

CarPlayManager already has a hook for customizing the set of map buttons in CarPlay, via the pass-through carPlayManager(_:mapButtonsCompatibleWith:in:for:) method. A similar method on NavigationViewControllerDelegate would be beneficial for the main screen. We could also adapt the MGLOrnamentPosition approach in mapbox/mapbox-gl-native#13911 to make it easy to move the stack of buttons around.

/cc @mapbox/navigation-ios