LatLngBounds southwest and northeast coordinate points were inverted, so
they could be extended via LatLngBounds::extend(). However, this looks
confusing and error-prone.
A static LatLngBounds::getExtendable() is added to address cases when we
want to extend LatLngBounds.
The location under your finger stays under your finger as you pan.
The location you double tap to zoom stays at the same point.
The location at the center of a pinch zoom stays at the center.
The location at the center of a rotation stays at the center.
