style: adjust mentions readonly cursor

[xrkffgg]

[中文版模板 / Chinese template]

🤔 This is a ...

• New feature
• Bug fix
• Site / documentation update
• Demo update
• Component style update
• TypeScript definition update
• Bundle size optimization
• Performance optimization
• Refactoring
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🔗 Related issue link

💡 Background and solution

📝 Changelog

Language	Changelog
🇺🇸 English	Adjusts Mentions readOnly mouse style to native style.
🇨🇳 Chinese	调整 Mentions readOnly 鼠标样式为原生样式。

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

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[ant-design-bot]

[ant-design-bot]

[xrkffgg]

@afc163 Mentions 的 readOnly 要动吗？现在是用的 default

[afc163]

可以改回来，readOnly 也可以复制文本的，应该用 text。

[github-actions]

Size Change: -59 B (0%)

Total Size: 785 kB

Filename	Size	Change
./dist/antd.compact.min.css	64.7 kB	-19 B (0%)
./dist/antd.dark.min.css	66 kB	-20 B (0%)
./dist/antd.min.css	64.7 kB	-20 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
./dist/antd-with-locales.min.js	311 kB	0 B
./dist/antd.min.js	279 kB	0 B

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