refactor: semantic font size variables

[guoyunhe]

将原本的 10 个非语义化的字体大小变量，合并为 5 个语义化的字体大小变量。

:root {
  --adm-font-size-1: 9px;
  --adm-font-size-2: 10px;
  // 合并为
  --adm-font-size-tiny: var(--adm-font-size-1);

  --adm-font-size-3: 11px;
  --adm-font-size-4: 12px;
  // 合并为
  --adm-font-size-small: var(--adm-font-size-3);

  --adm-font-size-5: 13px;
  --adm-font-size-6: 14px;
  // 合并为
  --adm-font-size-main: var(--adm-font-size-5);

  --adm-font-size-7: 15px;
  --adm-font-size-8: 16px;
  // 合并为
  --adm-font-size-large: var(--adm-font-size-8);

  --adm-font-size-9: 17px;
  --adm-font-size-10: 18px;
  // 合并为
  --adm-font-size-huge: var(--adm-font-size-10);
}

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.34%. Comparing base (784eff5) to head (b63cdce).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #6565 +/- ## ======================================= Coverage 92.34% 92.34% ======================================= Files 318 318 Lines 6910 6910 Branches 1729 1729 ======================================= Hits 6381 6381 Misses 493 493 Partials 36 36 ```

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[github-actions[bot]]

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