Track original SVG size (#7098)

This fixes bugs related to how an `Image` follows the size of an SVG.

We track the "source size" of each image, i.e. the original width/height
of the SVG, which can be different from whatever it was rasterized as.

crates/egui-wgpu/src/capture.rs

@@ -227,10 +227,10 @@ impl CaptureState {
             tx.send((
                 viewport_id,
                 data,
-                ColorImage {
-                    size: [tex_extent.width as usize, tex_extent.height as usize],
+                ColorImage::new(
+                    [tex_extent.width as usize, tex_extent.height as usize],
                     pixels,
-                },
+                ),
             ))
             .ok();
             ctx.request_repaint();