Fix SVG size calulation, only use style attribute (#36133)

Fixes: https://github.com/go-gitea/gitea/issues/35863

The old code had a conflict between using HTML attributes vs. style
properties where the style was overriding the previously set HTML
attributes:

```html
<img width="300" height="277.02439470988946" style="width: 275px; height: 0px;">
```

I made it so in all cases only `style` properties are used and the
previous width/height values are now set via `style`. Also I did a
number of much-needed typescript improvements to the file.

---------

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

web_src/css/repo/file-view.css

@@ -81,6 +81,7 @@
 .view-raw img[src$=".svg" i] {
   max-height: 600px !important;
   max-width: 600px !important;
+  background: var(--background-view-image);
 }
 
 .file-view-render-container {