servo: Merge #13058 - Response API (from malisas:malisa-responseAPI); r=Manishearth,jdm

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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).

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- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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Source-Repo: https://github.com/servo/servo
Source-Revision: 5a5a76cc5db830d2e622d4e0924837383b64dfa2

servo/components/script/dom/htmlscriptelement.rs

@@ -26,8 +26,6 @@ use dom::window::ScriptHelpers;
 use encoding::label::encoding_from_whatwg_label;
 use encoding::types::{DecoderTrap, EncodingRef};
 use html5ever::tree_builder::NextParserState;
-use hyper::http::RawStatus;
-use hyper_serde::Serde;
 use ipc_channel::ipc;
 use ipc_channel::router::ROUTER;
 use js::jsval::UndefinedValue;
@@ -159,7 +157,7 @@ impl AsyncResponseListener for ScriptContext {
 
         let status_code = self.metadata.as_ref().and_then(|m| {
             match m.status {
-                Some(Serde(RawStatus(c, _))) => Some(c),
+                Some((c, _)) => Some(c),
                 _ => None,
             }
         }).unwrap_or(0);