storyboard property
Mappings from GradientAnimations -> dynamic, where dynamic matches
with the key:
GradientAnimation.colorArithmetic:ColorArithmeticGradientAnimation.stopsArithmetic:StopsArithmeticGradientAnimation.tweenSpec: Map<GradientProperty, Tween<dynamic>>
Implementation
// - `GradientAnimation.tweenSpec: TweenSpec`
// - Where [TweenSpec] is a mapping from [GradientProperty]s -> [Tween]s
/// - `GradientAnimation.tweenSpec: Map<GradientProperty, Tween<dynamic>>`
final Map<GradientAnimation, dynamic> storyboard;