Auto merge of #29752 - mrobinson:fix-29741-by-extending-request-builder, r=mukilan

Fix 29741 by extending request builder

Extend RequestBuilder to include ResponseTainting and used said functionality to set response_tainting to `::CorsTainting` in `cors_preflight_fetch()`.

---
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- [x] These changes fix #29741
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components/net/http_loader.rs

@@ -1978,6 +1978,7 @@ async fn cors_preflight_fetch(
         .destination(request.destination.clone())
         .referrer_policy(request.referrer_policy)
         .mode(RequestMode::CorsMode)
+        .response_tainting(ResponseTainting::CorsTainting)
         .build();
 
     // Step 2