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/fonts/font_context.rs

@@ -661,7 +661,6 @@ impl RemoteWebFontDownloader {
             &core_resource_thread_clone,
             request,
             None,
-            None,
             Box::new(move |response_message| {
                 match downloader.handle_web_font_fetch_message(response_message) {
                     DownloaderResponseResult::InProcess => {},