* [ios] Don't animate zoom-induced accuracy ring size changes Improves perceived and actual performance by eliminating the implicit animation that occurred when the accuracy ring changed size during zooms. This previously would pile up animations as the zoom changed, causing an unsightly wobbling effect. * [ios] Pre-calculate shadow paths for user dot and puck Performance enhancement suggested by https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/CoreAnimation_guide/ImprovingAnimationPerformance/ImprovingAnimationPerformance.html * [ios] Rasterize pulsating inner dot of user location annotation Supposed performance enhancement and also improves edge smoothness.