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/base.css

@@ -39,6 +39,8 @@
 
   --gap-inline: 0.25rem; /* gap for inline texts and elements, for example: the spaces for sentence with labels, button text, etc */
   --gap-block: 0.5rem; /* gap for element blocks, for example: spaces between buttons, menu image & title, header icon & title etc */
+
+  --background-view-image: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAAG0lEQVQYlWN4+vTpf3SMDTAMBYXYBLFpHgoKAeiOf0SGE9kbAAAAAElFTkSuQmCC") right bottom var(--color-primary-light-7);
 }
 
 @media (min-width: 768px) and (max-width: 1200px) {

web_src/css/features/imagediff.css

@@ -13,7 +13,7 @@
 
 .image-diff-container img {
   border: 1px solid var(--color-primary-light-7);
-  background: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAAG0lEQVQYlWN4+vTpf3SMDTAMBYXYBLFpHgoKAeiOf0SGE9kbAAAAAElFTkSuQmCC") right bottom var(--color-primary-light-7);
+  background: var(--background-view-image);
 }
 
 .image-diff-container .before-container {

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 {