Auto merge of #13058 - malisas:malisa-responseAPI, r=Manishearth,jdm

Response API

<!-- Please describe your changes on the following line: -->
This PR adds the [dom::Response](https://fetch.spec.whatwg.org/#response-class) implementation and addresses #11896.

The relevant passing tests` expectations have been updated.

In order to allow non-UTF-8-encoded status messages, `net_traits::response::Response`'s `raw_status` field has been changed from type [`Option<RawStatus>`](https://doc.servo.org/hyper/http/struct.RawStatus.html) to type `Option<(u16, Vec<u8>)>`. As a result, a few other files which rely on the `raw_status` field were affected and updated.

TODOs:
- The `body` and `trailer` methods. Relies on implementation of `ReadableStream` and `Promise`s.
- Similarly, replace the dummy constructor `_body: Option<USVString>` argument with `body: ResponseBodyInit`.
- Currently, whenever `r's response's header list` or `r's Headers object` are mentioned, I always modify the `headers_reflector` field (of type dom::Headers, or `r's Headers object`) and not the corresponding hyper::Headers list in the net_traits::Response field. A completely accurate interpretation of the spec might consider making both of these lists the same thing via a reference. [Discussion](https://github.com/whatwg/fetch/issues/358) was [had](https://github.com/servo/servo/pull/12884).

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/13058)
<!-- Reviewable:end -->

tests/wpt/web-platform-tests/fetch/api/response/response-init-001.html

@@ -60,4 +60,4 @@
         }, "Check " + attributeName + " init values and associated getter");
     </script>
   </body>
-</html>
+</html>

tests/wpt/web-platform-tests/fetch/api/response/response-static-redirect.html

@@ -14,7 +14,7 @@
       var url = "http://test.url:1234/";
       test(function() {
         redirectResponse = Response.redirect(url);
-        assert_equals(redirectResponse.status, 302, "Default redictect status is 302");
+        assert_equals(redirectResponse.status, 302, "Default redirect status is 302");
         assert_equals(redirectResponse.headers.get("Location"), url,
           "redirected response has Location header with the correct url");
       }, "Check default redirect response");
@@ -23,7 +23,7 @@
       redirectStatus.forEach(function(status) {
         test(function() {
           redirectResponse = Response.redirect(url, status);
-          assert_equals(redirectResponse.status, status, "Redictect status is " + status);
+          assert_equals(redirectResponse.status, status, "Redirect status is " + status);
         }, "Check response returned by static method redirect(), status = " + status);
       });