feat: add Popover component

[chenjiahan]

#4142

[github-actions]

🎊 PR Preview 85202c7 has been successfully built and deployed to https://youzan-vant-preview-pr-7579.surge.sh

🕐 Build time: 86.811s

_{🤖 By surge-preview}

[codecov-io]

Codecov Report

Merging #7579 (8472ada) into 2.x (a766254) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              2.x    #7579      +/-   ##
==========================================
+ Coverage   90.79%   90.87%   +0.07%     
==========================================
  Files         179      180       +1     
  Lines        4902     4932      +30     
  Branches      295      295              
==========================================
+ Hits         4451     4482      +31     
+ Misses        414      413       -1     
  Partials       37       37              

Impacted Files	Coverage Δ
src/popover/index.js	100.00% <100.00%> (ø)
src/mixins/click-outside.js	100.00% <0.00%> (+14.28%)	⬆️

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