Vars to theme Menu

[mrgeorgegray]

• Adds vars for <Menu /> to default.less

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• Changes for master
• Make sure that you follow antd's code convention.
• Run npm run lint and fix those errors before submitting in order to keep consistent code style.
• Rebase before creating a PR to keep commit history clear.
• Add some descriptions and refer relative issues for you PR.

[codecov]

Codecov Report

Merging #9115 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #9115   +/-   ##
=======================================
  Coverage   85.26%   85.26%           
=======================================
  Files         195      195           
  Lines        4677     4677           
  Branches     1379     1379           
=======================================
  Hits         3988     3988           
  Misses        689      689

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