[w3c/ServiceWorker] Preserve sec-fetch-dest for passed navigate requests (Issue #1803)

ErikWitt created an issue (w3c/ServiceWorker#1803)

For navigate requests the `sec-fetch-dest` header is set to `document`. Once a service worker is introduced that simply forwards the request to the network, the `sec-fetch-dest` header changes to `empty`.

There are systems that rely on that header on server side to detect navigate requests and act accordingly. Shopify for example has some language/currency persistence logic that uses it.

Introducing a service worker that forwards requests (e.g. to cache responses for offline handling), breaks functionality.

I would argue that a navigate request from the browser should behave the same when proxied through a service worker. If this cannot be assumed by the developer, it gets very hard to implement service worker without potentially breaking functionality.

To have a reproducable example, here is a test website: https://dm-clone-optimized.app.baqend.com/fetch-dest/

It installs a service worker and when reloading you can see the `sec-fetch-dest` header being different depending on whether you bypass the service worker or not.

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