Auto merge of #14868 - bd339:iss14068, r=jdm

Fix loss of response type information in Fetch API

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Avoids mapping response types that are distinct according to [the spec](https://fetch.spec.whatwg.org/#concept-response-type) to fewer response types. Also updates test expectations to match that we now pass tests that check the response type.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #14068

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- [X] There are tests for these changes

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tests/unit/net/data_loader.rs

@@ -32,7 +32,7 @@ fn assert_parse(url:          &'static str,
             assert_eq!(header_content_type, content_type.as_ref());
 
             let metadata = match response.metadata() {
-                Ok(FetchMetadata::Filtered { filtered: FilteredMetadata::Transparent(m), .. }) => m,
+                Ok(FetchMetadata::Filtered { filtered: FilteredMetadata::Basic(m), .. }) => m,
                 result => panic!(result),
             };
             assert_eq!(metadata.content_type.map(Serde::into_inner), content_type);