The AttributedString that value or attributedValue will become after
a SemanticsAction.decrease action has been performed on this widget.
If a attributedDecreasedValue is provided, onDecrease must also be set
and there must either be an ambient Directionality or an explicit
textDirection must be provided.
Callers must not provide both decreasedValue and
attributedDecreasedValue, One or both must be null/// provided.
final AttributedString? attributedDecreasedValue;