✨ [Feature]: Table expand multi-column

[cbqqkcel]

What problem does this feature solve

1.比如我想点击商品名称展开，而不是箭头（且目前箭头还不能修改样式）
2.能支持多列展开。目前是联动的。点一个其他的箭头也会变

需求是：pdd后台的商品管理页面就是有多列展开的。

What does the proposed API look like

如上

[liguohuanb]

类似于excel的列分组组合，这个很有用，对于列多的表格，方便把列分组显示

[Issues-translate-bot]

Bot detected the issue body's language is not English, translate it automatically.

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Similar to Excel's column grouping combination, this is very useful. For tables with many columns, it is convenient to group and display columns.

[zzcr]

您好，感谢你的意见，我们内部评估下~~

[Issues-translate-bot]

Bot detected the issue body's language is not English, translate it automatically.

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Hello, thank you for your opinion, we will evaluate it internally~~

[gweesin]

1. 将 type="expand" 的插槽由默认插槽改成 name="expand" 的插槽
2. 默认插槽还是实现单元格内容，默认插槽提供触发 expand 的方法，将 click 展开 / 折叠交由应用端判断，如：

<template #default="{ click }">
  <custom-icon @click="click"></custom-icon>
</template>

这样可行，但会造成 BREAKING CHANGE

[Issues-translate-bot]

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1. Change the slot with type="expand" from the default slot to the slot with name="expand"
2. The default slot still implements cell content. The default slot provides a method to trigger expand, and the click expansion/collapse is left to the application side to judge, such as:

<template #default="{ click }">
  <custom-icon @click="click"></custom-icon>
</template>

This works, but will cause BREAKING CHANGE