A ScrollBehavior that will be applied to this widget individually.
Defaults to null, wherein the inherited ScrollBehavior is copied and modified to alter the viewport decoration, like Scrollbars.
ScrollBehaviors also provide ScrollPhysics. If an explicit ScrollPhysics is provided in physics, it will take precedence, followed by scrollBehavior, and then the inherited ancestor ScrollBehavior.
The ScrollBehavior of the inherited ScrollConfiguration will be modified by default to not apply a Scrollbar. This is because the NestedScrollView cannot assume the configuration of the outer and inner Scrollable widgets, particularly whether to treat them as one scrollable, or separate and desirous of unique behaviors.
final ScrollBehavior? scrollBehavior;