feat: Support scrollTo item index

[zombieJ]

In rc-select, we should support open to scroll to the active item:

listRef.current.scrollTo({ index: 233, align: 'auto' });

Support align:

• auto
• top
• bottom

[vercel]

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Latest deployment for this branch: https://rc-virtual-list-git-scroll-to.react-component.now.sh

[codecov]

Codecov Report

Merging #8 into master will increase coverage by 0.34%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master     #8      +/-   ##
========================================
+ Coverage   99.65%   100%   +0.34%     
========================================
  Files           5      5              
  Lines         289    343      +54     
  Branches       63     85      +22     
========================================
+ Hits          288    343      +55     
+ Misses          1      0       -1

Impacted Files	Coverage Δ
src/List.tsx	100% <100%> (ø)	⬆️
src/utils/algorithmUtil.ts	100% <0%> (+2.7%)	⬆️

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