feat: improve document for select/popover about `getPopupContainer` API

[so2liu]

中文模板 / Chinese Template

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What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update
• [ ] Refactor
• [ ] Test Case
• [ ] TypeScript definition update
• [x] Document improve
• [ ] CI/CD improve
• [ ] Branch sync
• [ ] Other, please describe:

PR description

Fixes #

Changelog

🇨🇳 Chinese

• Feat: 改善了select/popover组件中getPopupContainer的API描述，并给出了例子。参考了antd的文档，之前版本的文档只描述了这个API做什么，没有描述什么时候会用到，且不是那么直观。

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🇺🇸 English

• Feat: Improve the API description of getPopupContainer about select/popover element. And give an example. Refererence to antd document, previous version of document only describes the behavior of API, while the use situation is missing and without intuition.

Checklist

• [x] Test or no need
• [ ] Document or no need
• [ ] Changelog or no need

Other

• [ ] Skip Changelog

Additional information

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[codecov-commenter]

Codecov Report

Merging #754 (ab3dd2c) into main (44ff9e0) will increase coverage by 0.00%. The diff coverage is 100.00%.

:exclamation: Current head ab3dd2c differs from pull request most recent head 98fff88. Consider uploading reports for the commit 98fff88 to get more accurate results

@@           Coverage Diff           @@
##             main     #754   +/-   ##
=======================================
  Coverage   79.90%   79.90%           
=======================================
  Files         431      431           
  Lines       22093    22094    +1     
  Branches     5668     5668           
=======================================
+ Hits        17653    17654    +1     
  Misses       4419     4419           
  Partials       21       21           

Impacted Files	Coverage Δ
packages/semi-ui/tagInput/index.tsx	92.19% <ø> (ø)
packages/semi-foundation/tagInput/foundation.ts	91.20% <100.00%> (+0.09%)	:arrow_up:

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