fluro 转场动画源码
在使用自定义转场动画前，先扒一扒 fluro 的源码，通过源码可以发现这么一个标准的转场方法：
RouteTransitionsBuilder _standardTransitionsBuilder(TransitionType? transitionType) {return (BuildContext context, Animation<double> animation,Animation<double> secondaryAnimation, Widget child) {if (transitionType == TransitionType.fadeIn) {return FadeTransition(opacity: animation, child: child);} else {const Offset topLeft = const Offset(0.0, 0.0);const Offset topRight = const Offset(1.0, 0.0);const Offset bottomLeft = const Offset(0.0, 1.0);Offset startOffset = bottomLeft;Offset endOffset = topLeft;if (transitionType == TransitionType.inFromLeft) {startOffset = const Offset(-1.0, 0.0);endOffset = topLeft;} else if (transitionType == Tr
