Fix SVG side by side comparison link (#17375) (#17391)

Backport #17375

Define unique names for image tabs in pull requests, in order to toggle tabs correctly when multiple are displayed on one page.

Fixes position of swipe-bar so it does not overlay other UI components when scrolling.

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

Co-authored-by: Mario Lubenka <mario.lubenka@googlemail.com>

web_src/less/features/imagediff.less

@@ -54,7 +54,6 @@
       }
 
       .swipe-bar {
-        z-index: 100;
         position: absolute;
         height: 100%;
         top: 0;