feat(ui/select): support selected slot

[a145789]

Checklist

---

• Fix linting errors
• Tests have been added / updated (or snapshots)

Change information

Support select selected slots, can customize the selection style

[vercel]

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Name	Status	Preview	Comments	Updated
varlet	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Dec 31, 2022 at 3:43PM (UTC)
varlet-ui-playground	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Dec 31, 2022 at 3:43PM (UTC)

[codecov-commenter]

Codecov Report

Merging #806 (d15acbc) into dev (ffcfe60) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #806      +/-   ##
==========================================
+ Coverage   95.26%   95.33%   +0.07%     
==========================================
  Files         249      249              
  Lines        5677     5679       +2     
  Branches     1049     1050       +1     
==========================================
+ Hits         5408     5414       +6     
+ Misses        269      265       -4     

Impacted Files	Coverage Δ
packages/varlet-ui/src/select/Select.vue	96.52% <100.00%> (+0.02%)	⬆️
packages/varlet-ui/src/tooltip/Tooltip.vue	100.00% <0.00%> (ø)
packages/varlet-ui/src/menu/usePopover.ts	90.69% <0.00%> (+0.07%)	⬆️
...kages/varlet-ui/src/collapse-item/CollapseItem.vue	98.18% <0.00%> (+7.27%)	⬆️

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[haoziqaq]

please confirm test snapshot and update it