Match image file extensions case-insensitively (#8430)

`image.PNG` and `cat.SVG` were not recognized as images.

Adds `egui::load::has_extension(uri, extension)`, which ignores ASCII
case and any `#fragment`, and uses it for the `.svg`, `.gif`, `.webp`
and `.png` checks.

Note: gif/webp URIs like `a#b.gif` no longer match, since the fragment
is now excluded.

* [x] I have followed the instructions in the PR template

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/egui_extras/src/loaders/svg_loader.rs

@@ -29,7 +29,7 @@ impl SvgLoader {
 }
 
 fn is_supported(uri: &str) -> bool {
-    uri.ends_with(".svg")
+    egui::load::has_extension(uri, "svg")
 }
 
 impl Default for SvgLoader {