DecorationTween constructor
Creates a decoration tween.
The begin and end properties may be null. If both are null, then the
result is always null. If end is not null, then its lerping logic is
used (via Decoration.lerpTo). Otherwise, begin's lerping logic is used
(via Decoration.lerpFrom).
Implementation
DecorationTween({ Decoration begin, Decoration end }) : super(begin: begin, end: end);