fix(components): [tabs] Layout issues

[Yolo-00]

修复 tabs 组件 addable 设置为 true 时导致的布局问题
fix #16835

[pull-request-triage]

👋 @Yolo-00, seems like this is your first time contribution to element-plus.

• Please make sure that you have read our guidelines and code of conduct before making a contribution.
• You can comment with /label Components:[component_name] to add a label for which component you are working on.
• You may join our for staying tuned.

[github-actions]

[github-actions]

Hello @Yolo-00, thank you for contributing to element-plus, please see our guideline to see how to make contribution

[github-actions]

🧪 Playground Preview: https://element-plus.run/?pr=16894
Please comment the example via this playground if needed.

[btea]

There is also a problem with your adjusted layout. The add button should be at the bottom.

[Yolo-00]

1. 当前pr修复的是 tabs 组件 addable 为 true ，tab-position 为 left 时导致的 添加按钮布局问题

2. 之前的线上版本设计的是 tab-position 为 right 时 添加按钮在右侧显示，所以我以为 left 时应该在左侧

[Yolo-00]

目前的组件设计好像也不太满足添加按钮放置底部的设计

[btea]

According to my understanding, perhaps it should be added below. But it seems a bit strange, so let's ask more people for their opinions. cc @element-plus/backers

[Yolo-00]

我调研了几个别的组件库，他们的设计理念是 不管 tabs 所在位置是 top || right || bottom || left ， 他们的新增按钮都是跟随在选项卡后面的

[btea]

在左侧的时候我们可以考虑新增按钮放在选项卡下面，默认情况不变。

[Yolo-00]

这样的布局是否可以接受？

[btea]

看起来可以。 👍