fix(comp:*): the font size under seer theme is incorrect

[danranVm]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines
• Tests for the changes have been added/updated or not needed
• Docs and demo have been added/updated or not needed

What is the current behavior?

• 部分组件受 reset-component 的影响，在 seer 主题下字体大小是 14px

What is the new behavior?

• 新增了 --ix-font-size 作为全局的字体变量，default 为 14px, seer 为 12px 彻底解决字体问题。

Other information

[idux-bot]

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[codecov]

Codecov Report

Merging #1343 (c1dcc7f) into main (6eeffb8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1343   +/-   ##
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  Coverage   93.09%   93.09%           
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  Files         323      323           
  Lines       29912    29912           
  Branches     3394     3394           
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  Hits        27848    27848           
  Misses       2064     2064           

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