Use image cache to stop leaking images (#29452)

This PR fixes several possible memory leaks due to loading images in
markdown files and the image viewer, using the new image cache APIs

TODO: 
- [x] Ensure this didn't break rendering in any of the affected
components.

Release Notes:

- Fixed several image related memory leaks

crates/markdown_preview/src/markdown_renderer.rs

@@ -139,7 +139,6 @@ pub fn render_parsed_markdown(
             .map(|block| render_markdown_block(block, &mut cx)),
     )
 }
-
 pub fn render_markdown_block(block: &ParsedMarkdownElement, cx: &mut RenderContext) -> AnyElement {
     use ParsedMarkdownElement::*;
     match block {