Set if the event was synthesized by Flutter.
We occasionally synthesize PointerEvents that aren't exact translations
ui.PointerData from the engine to cover small cross-OS discrepancies
in pointer behaviors.
For instance, on end events, Android always drops any location changes that happened between its reporting intervals when emitting the end events.
On iOS, minor incorrect location changes from the previous move events can be reported on end events. We synthesize a PointerEvent to cover the difference between the 2 events in that case.
final bool synthesized