perf(List): remove Flex usage

[layershifter]

⚠️ Do not use Flex in components in internals

Similar to #2023.

Any Stardust component will add additional style computations (merging, resolving) and will create performance degrade. One more reason to do not use Flexes: styles of Flex are not part of component so there is no way to generate static styles from if it used.

🚀 Measures

The test example below contains the worse scenario when all previously used Flexes will be rendered.

import * as _ from 'lodash'
import * as React from 'react'
import { List } from '@stardust-ui/react'

const items = _.times(100, i => ({
  key: i,
  media: 'Media',
  header: 'Foo',
  headerMedia: 'Bar',
  content: 'Baz',
  contentMedia: 'Qux',
}))

const ListPerf = () => <List items={items} />

export default ListPerf

Diff is around 39%. As ListItem is used in Dropdown, it should get performance benefits.

Before

Example	Avg	Median
List.perf.tsx	194.48	193.65

After

Example	Avg	Median
List.perf.tsx	131.42	130.44

[codecov]

Codecov Report

Merging #2025 into master will increase coverage by 7.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2025      +/-   ##
==========================================
+ Coverage   68.52%   75.57%   +7.04%     
==========================================
  Files         910      160     -750     
  Lines        8306     5567    -2739     
  Branches     2438     1609     -829     
==========================================
- Hits         5692     4207    -1485     
+ Misses       2600     1346    -1254     
  Partials       14       14

Impacted Files	Coverage Δ
packages/react/src/components/List/ListItem.tsx	100% <100%> (ø)	⬆️
packages/react/src/components/Flex/FlexItem.tsx	7.14% <0%> (-71.43%)	⬇️
packages/react/src/components/Flex/Flex.tsx	80% <0%> (-20%)	⬇️
...ckages/react/src/components/Popup/PopupContent.tsx	95.45% <0%> (-4.55%)	⬇️
...ges/react/src/components/Attachment/Attachment.tsx	87.5% <0%> (-3.81%)	⬇️
...es/react/src/components/Tooltip/TooltipContent.tsx	100% <0%> (ø)	⬆️
packages/react/src/index.ts	100% <0%> (ø)	⬆️
...s/components/RadioGroup/radioGroupItemVariables.ts
...mponents/Icon/svg/ProcessedIcons/icons-zoom-in.tsx
.../components/Icon/svg/ProcessedIcons/icons-hand.tsx
... and 762 more

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