[core, ios, osx] Tilt around visual center point

The tilt gesture on both iOS and OS X now respects the content insets. On iOS, in user tracking mode, it additionally respects the user dot’s position if it’s aligned to the top or bottom of the view.

include/mbgl/map/map.hpp

@@ -130,6 +130,7 @@ public:
 
     // Pitch
     void setPitch(double pitch, const Duration& = Duration::zero());
+    void setPitch(double pitch, const PrecisionPoint&, const Duration& = Duration::zero());
     double getPitch() const;
 
     // North Orientation