fix: input textarea hadle when has affix

[xrkffgg]

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[中文版模板 / Chinese template]

This is a ...

• New feature
• Bug fix
• Site / document update
• Component style update
• TypeScript definition update
• Refactoring
• Code style optimization
• Branch merge
• Other (about what?)

What's the background?

fix #2486

What's the effect? (Optional if not new feature)

• 向下拖动正常
• 无法向上拖动

#	Preview
Before ❌
After ✅

Changelog description (Optional if not new feature)

-	changelog
EN	Fix the problem that Input textarea cannot drag upward when allow-clear is activated.
CN	修复 Input textarea 激活 allow-clear 时无法向上拖动的问题。

Self Check before Merge

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

Additional Plan? (Optional if not new feature)

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