Use flex to align SVG and text (#25163) (#25260)

Use flex to align SVG and text (#25163) (#25260)

Backport #25163 by @wxiaoguang

The code can be as simple as:

```html
<div class="flex-text-block">{{svg "octicon-alert"}} {{svg "octicon-x"}} text (block)</div>
<div><div class="flex-text-inline">{{svg "octicon-alert"}} {{svg "octicon-x"}} text</div> (inline)</div>
<div><button class="ui red button">{{svg "octicon-alert" 24}} {{svg "octicon-x" 24}} text</button></div>
```

![image](https://github.com/go-gitea/gitea/assets/2114189/1d3c10f1-0bc7-4c26-b236-bad537d5c465)

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>