onUpdate property Null safety
A pointer is in contact with the screen and is either moving on the plane of the screen, pressing the screen with varying forces or both simultaneously.
This callback will be invoked for every pointer event after the invocation
of onStart and/or onPeak and before the invocation of onEnd, no
matter what the pressure is during this time period. The position and
pressure of the pointer is provided in the callback's
which is a ForcePressDetails object.