pointNumber passed to Plotly.Fx.Hover() is not used for box plots

When attempting to build off of the Coupled Hover Events example, I've found that box plots don't appear to make use of the pointNumber property of evt. I did find a workaround that uses xval and yval, but, in addition to being a bit more verbose, it can cause the wrong point to highlight if several are close / overlapping, so some way to specify particular points still seems useful.

https://codepen.io/cszucko/pen/gONaZqd

使用链接的 Coupled Hover Events 示例和 CodePen 重现该问题，重点关注 Plotly.Fx.Hover() 与箱线图的配合。将 pointNumber 的行为与 xval/yval workaround 进行比较；当 pointNumber 能够可靠地高亮指定的箱线图数据点（包括数据点重叠时）时，即表示完成。