Add spec steps and comments for fetch abort steps (#39283)

While trying to figure out what the status of this implementation was, I
added steps and comments to
see what we are missing. Also updated some links,
since I couldn't find an implementation of
`window.fetch`, since the spec URL was pointing
to the chapter instead of the algorithm.

Part of #34866

Signed-off-by: Tim van der Lippe <tvanderlippe@gmail.com>

components/script/dom/window.rs

@@ -1798,7 +1798,7 @@ impl WindowMethods<crate::DomTypeHolder> for Window {
         mql
     }
 
-    // https://fetch.spec.whatwg.org/#fetch-method
+    /// <https://fetch.spec.whatwg.org/#dom-global-fetch>
     fn Fetch(
         &self,
         input: RequestOrUSVString,