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] These changes fix#14068
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- [X] There are tests for these changes
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f1c82be0e6
