The value that value or attributedValue will become after a
SemanticsAction.increase action has been performed on this widget.
If a value is provided, onIncrease must also be set and there must
either be an ambient Directionality or an explicit textDirection
must be provided.
Callers must not provide both increasedValue and
attributedIncreasedValue, One or both must be null.
final String? increasedValue;