[fetch] allow opaqueredirect to be returned for any Request with "manual" RedirectMode (#127)

Currently we allow `fetch(url, { redirect: 'manual' })` which can return an opaque-redirect Response.  This works fine, unless intercepted by a SW that does `e.respondWith(fetch(e.request))`.  Then it breaks because we only allow passing opaque-redirect Responses to respondWith() if the request is a navigation.

We should consider allowing opaqueredirect for any Request with a "manual" RedirectMode.

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fetch/issues/127