fix: [editor] Fix the replaceRange interface issue

[Kakueeen]

as title

Log: fix issue

[deepin-ci-robot]

deepin pr auto review

关键摘要:

• 代码中使用了lineText.length()来获取行长度，但没有考虑到多字节字符的情况，可能会导致中文等字符被错误地计算为多个字符长度。
• replaceRange函数中的注释提到了lineLength()函数计算的是字节长度，但没有提供解决方案来处理多字节字符的情况。

是否建议立即修改:

• 是

建议的修改措施:

• 使用editor->toPlainText().length()来获取行长度，确保正确处理多字节字符。
• 如果需要处理特定字符集的长度，可以考虑使用editor->toPlainText().toUtf8().length()来获取字节数，但要注意这可能会导致性能问题。
• 在注释中提供解决方案，例如使用editor->toPlainText().length()来替代lineLength()，并确保文档中说明如何处理多字节字符。

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: deepin-mozart, Kakueeen

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