Add the possibility to pass a custom Clipper to the slidable

[HeronAmilon]

Transform that class in an abstract one and become an optional parameter to the Slidable, i'm struggling to make some custom animations in my code using the package without this customization:

class _SlidableClipper extends CustomClipper<Rect> {
  _SlidableClipper({
    required this.axis,
    required this.controller,
  }) : super(reclip: controller.animation);

  final Axis axis;
  final SlidableController controller;

  @override
  Rect getClip(Size size) {
    switch (axis) {
      case Axis.horizontal:
        final double offset = controller.ratio * size.width;
        if (offset < 0) {
          return Rect.fromLTRB(size.width + offset, 0, size.width, size.height);
        }
        return Rect.fromLTRB(0, 0, offset, size.height);
      case Axis.vertical:
        final double offset = controller.ratio * size.height;
        if (offset < 0) {
          return Rect.fromLTRB(
            0,
            size.height + offset,
            size.width,
            size.height,
          );
        }
        return Rect.fromLTRB(0, 0, size.width, offset);
    }
  }

  @override
  Rect getApproximateClipRect(Size size) => getClip(size);

  @override
  bool shouldReclip(_SlidableClipper oldClipper) {
    return oldClipper.axis != axis;
  }
}