URL-encoded URLs not decoded

Nobody has claimed this yet.

While investigating why [KiCAD's project icon is not rendering properly in some renders](https://gitlab.com/kicad/code/kicad/-/blob/332b4ed1078a2c06d3be08d2f737d1a57e764c07/resources/linux/icons/hicolor/scalable/mimetypes/application-x-kicad-project.svg) I discovered that resvg *is* one of the renderers in question.

The culprit seems to be in [line 650](https://gitlab.com/kicad/code/kicad/-/blob/332b4ed1078a2c06d3be08d2f737d1a57e764c07/resources/linux/icons/hicolor/scalable/mimetypes/application-x-kicad-project.svg)
```
style="fill:url(#%D0%91%D0%B5%D0%B7%D1%8B%D0%BC%D1%8F%D0%BD%D0%BD%D1%8B%D0%B9_%D0%B3%D1%80%D0%B0%D0%B4%D0%B8%D0%B5%D0%BD%D1%82_10);stroke-width:1" />
```

After running the argument to `url()` through URL decoding, we get `#Безымянный_градиент_10`, and `Безымянный_градиент_10` is a gradient present on line 456.

I'm not deep enough into various W3C specs to say for sure if that should be decoded, but I think it should. Chromium (whatever it uses for SVG), Thunar (qt6-svg, I think) and Inkscape render the file correctly, while rsvg seems to have the exact same issue. Firefox too, but I think it uses rsvg?

Use the KiCAD SVG linked in the report, especially the fill URL on line 650 and the matching gradient on line 456. Trace resvg's handling of the percent-encoded fragment in url(), then verify that the SVG renders its project icon correctly when the fragment identifies that gradient.

Written by the indexing model from the issue text.