fix(components): [tabs] optimize SSR

[makedopamine]

fixes #15088

before

after

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[github-actions]

[github-actions]

Hello @makedopamine, 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=15183
Please comment the example via this playground if needed.

[tolking]

LGTM.

[qcyblm]

@tolking Looking forward to seeing the update merge. Any idea when it will be pushed?

[btea]

There are code conflicts that need to be resolved.

[makedopamine]

There are code conflicts that need to be resolved.

Resolved

[kaine0923]

tab-position value is top by default, that is, the header in the upper panels in the lower, why do we default the header in the lower, and then use flex-direction: column-reverse to go to the inverse again

[makedopamine]

The reason had been mentioned in the above comment.

[zhixiaotong]

@btea @tolking 这个pr导致了tabs的内容发生了改变，属于breaking change了。正常content在header下面，现在这个content在header上面了，然后又加了一个flex-direction: column-reverse;保证正常，但影响了原有的项目，升级新版本后，发现项目原有好多样式需要重写，影响蛮大的。

[tolking]

这个PR是属于breaking chang，所以才会在v2.8.0 合并。

对于普通用户来说影响应该挺小的。

[zhixiaotong]

也许我们应该在changelog中体现这些变更的细节。
我习惯性在tabs下使用纵向flex布局，在升级之前一般会先看changlog，但问题发生才回溯代码发现是某些原因，之前也有几次升级出现过类似的问题。
我以前看过一些issue风评不好，这会导致用户在选择升级版本变得更加不确定。

[btea]

@zhixiaotong 多谢反馈，后续我们会尝试优化这方面的工作。