Auto merge of #21111 - gterzian:implement_document_load_cancellation, r=jdm

Implement document load cancellation

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- [ ] `./mach build -d` does not report any errors
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- [ ] These changes fix #19309 fix #21114 fix #21113 (github issue number if applicable).

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components/script/dom/htmlimageelement.rs

@@ -300,7 +300,7 @@ impl HTMLImageElement {
 
         // This is a background load because the load blocker already fulfills the
         // purpose of delaying the document's load event.
-        document.loader().fetch_async_background(request, action_sender);
+        document.loader_mut().fetch_async_background(request, action_sender);
     }
 
     /// Step 14 of https://html.spec.whatwg.org/multipage/#update-the-image-data