gpui: Maintain img aspect ratio when max_width is set (#25632)

Release Notes:

- Fixed Markdown preview to display image with max width 100%.

## Before

<img width="1202" alt="image"
src="https://github.com/user-attachments/assets/359628df-8746-456f-a768-b3428923c937"
/>
<img width="750" alt="SCR-20250226-napv"
src="https://github.com/user-attachments/assets/f6154516-470e-41b2-84f5-ef0612c447ad"
/>


## After

<img width="1149" alt="image"
src="https://github.com/user-attachments/assets/2279347d-9c69-4a47-bb62-ccc8e55a98f6"
/>
<img width="520" alt="SCR-20250226-ngyz"
src="https://github.com/user-attachments/assets/03af5f14-1935-472e-822f-4c7f62630780"
/>

crates/markdown_preview/src/markdown_renderer.rs

@@ -513,12 +513,16 @@ fn render_markdown_text(parsed_new: &MarkdownParagraph, cx: &mut RenderContext)
                 let image_element = div()
                     .id(element_id)
                     .cursor_pointer()
-                    .child(img(ImageSource::Resource(image_resource)).with_fallback({
-                        let alt_text = image.alt_text.clone();
-                        {
-                            move || div().children(alt_text.clone()).into_any_element()
-                        }
-                    }))
+                    .child(
+                        img(ImageSource::Resource(image_resource))
+                            .max_w_full()
+                            .with_fallback({
+                                let alt_text = image.alt_text.clone();
+                                {
+                                    move || div().children(alt_text.clone()).into_any_element()
+                                }
+                            }),
+                    )
                     .tooltip({
                         let link = image.link.clone();
                         move |_, cx| {