Depending on the platform and specific trackpad model, the new system might not
be used, if not enough data is provided to the Flutter engine by platform APIs.
This includes on Windows, where trackpad gesture support is dependent on the
trackpad’s driver, and the Web platform, where not enough data is provided by
browser APIs, and trackpad scrolling must still use the old `PointerScrollSignal
system.

Developers should be prepared to receive both types of events and ensure their apps
or packages handle them in the appropriate manner.

Listener now has three new callbacks: onPointerPanZoomStart,
onPointerPanZoomUpdate, and onPointerPanZoomEnd which can be used to observe
trackpad scrolling and zooming events.

void

main

()

runApp

Foo

());

class

Foo

extends

StatelessWidget

@override

Widget