Scrolling on the legend will cause the parent to scroll

When I scroll in the legend, the whole page scrolls as long as the legend is at the top or bottom. This seems to be normal, but the problem is that it scrolls so fast that it quickly reaches the top or bottom and scrolls the whole page.

I found out it was a bug in the source code makes the scroll so fast, which I checked and fixed with PR #7067 (I'm not sure if my fix is correct, but the scrolling behavior got much better.

The current legend scroll behavior with Plotly v2.34.0:
it reaches the bottom or top quickly and make the page scroll!

Note that I'm using Windows 10 with lines to scroll set to 10 each time, but I think 10 isn't that high:

After my fix in the source code, scrolling becomes normal with lines to scroll set to 10:

And even normal if the value for the lines to be scrolled is set to 1:

P.S. In the PR #7067, I would prefer the page to stop scrolling at the top or bottom of the legend as well, since the original behavior scrolls the page immediately when it reaches the top or bottom, as opposed to the native browser behavior where you have to scroll again to scroll the parent.

P.S. The touch event also seems to have a problem, when touch dragging the legend the whole page moves.
But in the PR #7067 for solving this issue, I only focus on the wheel scroll event.

首先检查 PR #7067 以及 Plotly v2.34.0 中对 legend wheel-scroll 的处理。使用所述的 Windows 滚轮设置重现该问题，然后比较图例边界处的滚轮行为。完成的标准是滚动图例时页面不再意外移动；触摸行为单独考虑。