:sparkles: feat: change all default size as middle & update FieldSet doc

[github-actions[bot]]

🎊 PR Preview 92d12aa9795ff5bcbc6450c86c2890120a08c275 has been successfully built and deployed to https://ant-design-pro-editor-preview-pr-116.surge.sh

:clock1: Build time: 78.206s

_{🤖 By surge-preview}

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Codecov Report

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

Comparison is base (ac27441) 80.96% compared to head (92d12aa) 80.97%. Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #116 +/- ## ========================================== + Coverage 80.96% 80.97% +0.01% ========================================== Files 415 416 +1 Lines 25569 25590 +21 Branches 1156 1159 +3 ========================================== + Hits 20701 20722 +21 Misses 4868 4868 ```

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:tada: This PR is included in version 0.31.0 :tada:

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