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/net/http_loader.rs

@@ -1944,7 +1944,7 @@ async fn http_network_fetch(
     let meta_status = meta.status;
     let meta_headers = meta.headers;
     let cancellation_listener = context.cancellation_listener.clone();
-    if cancellation_listener.lock().unwrap().cancelled() {
+    if cancellation_listener.cancelled() {
         return Response::network_error(NetworkError::Internal("Fetch aborted".into()));
     }
 
@@ -1983,7 +1983,7 @@ async fn http_network_fetch(
                 warn!("Error streaming response body: {:?}", e);
             })
             .try_fold(res_body, move |res_body, chunk| {
-                if cancellation_listener.lock().unwrap().cancelled() {
+                if cancellation_listener.cancelled() {
                     *res_body.lock().unwrap() = ResponseBody::Done(vec![]);
                     let _ = done_sender.send(Data::Cancelled);
                     return future::ready(Err(()));