内置的PointSelector不适合用于计算饼图/日出图等带角度的图表的选中域，能否将Selector开放到Selection中做参数以方便定制化？

[XiFengLang]

PointSelector用2点之间的距离筛选出nearestDistance（代码如下），这套算法在饼图和日出图中会算出错误的nearestIndex，导致tooltip展示异常。我还没来得及学习Graphic专业知识，不清楚作者后续是否会增加一个判断角度的AngleSelector，如果Graphic专业领域中不需要AngleSelector，那希望作者开放更多的定制接口，以方便其他开发者定制图表功能。

    final point = coord.invert(points.single);
    if (dim == null) {
      updateNearest = (attributes) {
        final offset = attributes.representPoint - point;
        // The neighborhood is an approximate square.
        final distance = (offset.dx.abs() + offset.dy.abs()) / 2;
        if (distance < nearestDistance) {
          nearestIndex = attributes.index;
          nearestDistance = distance;
        }
      };
    } else {
      final getProjection = dim == Dim.x
          ? (Offset offset) => offset.dx
          : (Offset offset) => offset.dy;
      updateNearest = (attributes) {
        final p = attributes.representPoint;
        final distance = (getProjection(point) - getProjection(p)).abs();
        if (distance < nearestDistance) {
          nearestIndex = attributes.index;
          nearestDistance = distance;
        }
      };
    }