Add Image::uri() (emilk#4720)

`uri()` for image

The advantages of this are :

1. No need for `ctx()` and `source()`
2. Displays `name.gif#0` as `name.gif`

crates/egui/src/widgets/image.rs

@@ -283,6 +283,20 @@ impl<'a> Image<'a> {
         }
     }
 
+    /// Returns the URI of the image.
+    ///
+    /// For GIFs, returns the URI without the frame number.
+    #[inline]
+    pub fn uri(&self) -> Option<&str> {
+        let uri = self.source.uri()?;
+
+        if let Ok((gif_uri, _index)) = decode_gif_uri(uri) {
+            Some(gif_uri)
+        } else {
+            Some(uri)
+        }
+    }
+
     #[inline]
     pub fn image_options(&self) -> &ImageOptions {
         &self.image_options