fix: 修复删除多个文件夹时确认按钮不显示加载态的问题，并减少删除时不必要的basedir请求

[wangdage12]

What this PR does / why we need it?

在删除大量文件夹时，删除对话框的确认按钮不会变为加载态，这会让用户以为删除操作始终未开始，影响用户操作，如果用户继续点击会出现大量并发重复的删除请求。
另外，删除每个文件夹时都会请求basedirapi，在删除多个文件夹时会造成大量重复请求。

Summary of your change

• 为按钮添加加载态，loading.value = true;原来的位置有问题，已提前至删除操作的顶部
• 每次整个删除操作只请求一次basedir

Please indicate you've done the following:

• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

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[lan-yonghui]

/lgtm