net: Use RequestId to cancel fetches instead of creating an IPC channel (#34883)

Instead of creating an IPC channel for every fetch, allow cancelling
fetches based on the `RequestId` of the original request. This requires
that `RequestId`s be UUIDs so that they are unique between processes
that might communicating with the resource process.

In addition, the resource process loop now keeps a `HashMap` or `Weak`
handles to cancellers and cleans them up.

This allows for creating mutiple `FetchCanceller`s in `script` for a
single fetch request, allowing integration of the media and video
elements to integrate with the `Document` canceller list -- meaning
these fetches also get cancelled when the `Document` unloads.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/htmlimageelement.rs

@@ -419,7 +419,7 @@ impl HTMLImageElement {
 
         // This is a background load because the load blocker already fulfills the
         // purpose of delaying the document's load event.
-        document.fetch_background(request, context, None);
+        document.fetch_background(request, context);
     }
 
     // Steps common to when an image has been loaded.