slide method
Adds a SlideEffect that moves the target based on a fraction of its size
per the specified begin and end offsets (via SlideTransition).
Implementation
T slide({
  Duration? delay,
  Duration? duration,
  Curve? curve,
  Offset? begin,
  Offset? end,
}) =>
    addEffect(SlideEffect(
      delay: delay,
      duration: duration,
      curve: curve,
      begin: begin,
      end: end,
    ));