Whether the scrollable should let the user adjust the scroll offset, for example by dragging.
By default, the user can manipulate the scroll offset if, and only if, there is actually content outside the viewport to reveal.
position is only valid during this method call. Do not keep a
reference to it to use later, as the values may update, may not update, or
may update to reflect an entirely unrelated scrollable.
@override bool shouldAcceptUserOffset(ScrollMetrics position) => false;