[WIP] Support animation

[zombieJ]

We use class component here since typescript can not support generic in function component

Virtual list display logic:

1. scroll / initialize trigger measure
2. Get location item of current scrollTop
3. [Render] Render visible items
4. Get all the visible items height
5. [Render] Update top item margin-top to fit the position

Algorithm

We split scroll bar into equal slice. An item with whatever height occupy the same range slice.
When scrollTop change, it will calculate the item percentage position and move item to the position.
Then calculate other item position base on the located item.

Concept

located item

The base position item which other items position calculate base on.

[vercel]

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

[codecov]

Codecov Report

Merging #2 into master will increase coverage by 14.6%.
The diff coverage is 16.33%.

@@            Coverage Diff            @@
##           master      #2      +/-   ##
=========================================
+ Coverage       0%   14.6%   +14.6%     
=========================================
  Files           3       4       +1     
  Lines          71     226     +155     
  Branches       12      46      +34     
=========================================
+ Hits            0      33      +33     
- Misses         71     192     +121     
- Partials        0       1       +1

Impacted Files	Coverage Δ
src/Filler.tsx	0% <0%> (ø)	⬆️
src/utils/itemUtil.ts	0% <0%> (ø)
src/List.tsx	0% <0%> (ø)	⬆️
src/utils/algorithmUtil.ts	94.28% <94.28%> (ø)

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[zombieJ]

Preview: https://rc-virtual-list-git-animation.react-component.now.sh/iframe.html?selectedKind=rc-virtual-list&selectedStory=animate

cc @afc163 Please help to check on this.