docs(vue): add more scopedSlot content tests and readme

[rayy-li]

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• Ensure the pull request title and commit message follow the Commit Specific in English.
• Fork the repo and create your branch from master or formily_next.
• If you've added code that should be tested, add tests!
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What have you changed?

add tests and some readme document for #2221

[codecov]

Codecov Report

Merging #2226 (50c87b7) into formily_next (2489182) will not change coverage.
The diff coverage is n/a.

@@              Coverage Diff              @@
##           formily_next    #2226   +/-   ##
=============================================
  Coverage         95.31%   95.31%           
=============================================
  Files               138      138           
  Lines              6169     6169           
  Branches           1555     1555           
=============================================
  Hits               5880     5880           
  Misses              284      284           
  Partials              5        5           

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