Add basic ico support (#40822)

Closes https://github.com/zed-industries/zed/discussions/40763

<img width="867" height="1088" alt="Screenshot 2025-10-21 at 23 14 47"
src="https://github.com/user-attachments/assets/d691fb2a-afc6-4445-a335-054ef164e0d3"
/>

Also improves error handling on image open failure:

<img width="864" height="1083" alt="Screenshot 2025-10-21 at 23 14 30"
src="https://github.com/user-attachments/assets/d5388b61-995f-441b-b375-ad5136d1533b"
/>


Release Notes:

- Added basic ico support, improved unsupported image handling

crates/gpui/src/platform.rs

@@ -1644,6 +1644,8 @@ pub enum ImageFormat {
     Bmp,
     /// .tif or .tiff
     Tiff,
+    /// .ico
+    Ico,
 }
 
 impl ImageFormat {
@@ -1657,6 +1659,7 @@ impl ImageFormat {
             ImageFormat::Svg => "image/svg+xml",
             ImageFormat::Bmp => "image/bmp",
             ImageFormat::Tiff => "image/tiff",
+            ImageFormat::Ico => "image/ico",
         }
     }
 
@@ -1670,6 +1673,7 @@ impl ImageFormat {
             "image/svg+xml" => Some(Self::Svg),
             "image/bmp" => Some(Self::Bmp),
             "image/tiff" | "image/tif" => Some(Self::Tiff),
+            "image/ico" => Some(Self::Ico),
             _ => None,
         }
     }
@@ -1776,6 +1780,7 @@ impl Image {
             ImageFormat::Webp => frames_for_image(&self.bytes, image::ImageFormat::WebP)?,
             ImageFormat::Bmp => frames_for_image(&self.bytes, image::ImageFormat::Bmp)?,
             ImageFormat::Tiff => frames_for_image(&self.bytes, image::ImageFormat::Tiff)?,
+            ImageFormat::Ico => frames_for_image(&self.bytes, image::ImageFormat::Ico)?,
             ImageFormat::Svg => {
                 let pixmap = svg_renderer.render_pixmap(&self.bytes, SvgSize::ScaleFactor(1.0))?;