fix: optimize the shadow effect of Scrollable

[mortalYoung]

简介

• 修复滚动组件的阴影渲染时机不对的问题

主要变更

• 在 scrollStart 取应该是不合理的，只能拿到每次滚动开始才会渲染阴影，而实际上应该在滚动的时候实时去判断是否渲染

[codecov]

Codecov Report

Merging #443 (052decb) into main (50e0de2) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #443   +/-   ##
=======================================
  Coverage   80.76%   80.76%           
=======================================
  Files         177      177           
  Lines        4908     4908           
  Branches     1062     1062           
=======================================
  Hits         3964     3964           
  Misses        935      935           
  Partials        9        9           

Impacted Files	Coverage Δ
src/components/scrollable/index.tsx	100.00% <100.00%> (ø)

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[mortalYoung]

这个组件的 onScroll 这个函数测试不到 0.0 有啥办法吗 @wewoor

[wewoor]

这个组件的 onScroll 这个函数测试不到 0.0 有啥办法吗 @wewoor

可以使用

/* istanbul ignore next */

注释忽略

[wewoor]

�暂时无法 mock 的测试，先忽略掉

[wewoor]

+1