Auto merge of #13345 - malisas:malisa-bodyAPI, r=jdm

implement Body for dom::Response and dom::Request

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This PR adds dom::Response and dom::Request's `Text()`, `Blob()`, `Json()`, and (part of the) `FormData()` functions, part of the [Body mixin](https://fetch.spec.whatwg.org/#body). The corresponding tests have also been updated as passing.

@jeenalee also contributed to this PR, primarily the `Blob()`, `Json()`, and `FormData()` implementations.

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- [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).

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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components/script/dom/webidls/Body.webidl

@@ -10,10 +10,9 @@
 interface Body {
   readonly attribute boolean bodyUsed;
 
-  // Servo does not support Promise at this moment.
   // [NewObject] Promise<ArrayBuffer> arrayBuffer();
-  // [NewObject] Promise<Blob> blob();
-  // [NewObject] Promise<FormData> formData();
-  // [NewObject] Promise<JSON> json();
-  // [NewObject] Promise<USVString> text();
+  [NewObject] Promise<Blob> blob();
+  [NewObject] Promise<FormData> formData();
+  [NewObject] Promise<any> json();
+  [NewObject] Promise<USVString> text();
 };

components/script/dom/webidls/Response.webidl

@@ -4,8 +4,7 @@
 
 // https://fetch.spec.whatwg.org/#response-class
 
-// TODO: pass 'optional ResponseBodyInit? body = null' to constructor in place of USVString
- [Constructor(optional USVString? body = null, optional ResponseInit init),
+ [Constructor(optional BodyInit? body = null, optional ResponseInit init),
   Exposed=(Window,Worker)]
 interface Response {
   [NewObject] static Response error();