[feat] dev time service workers

[Rich-Harris]

Closes #5479. In development, this intercepts requests for /service-worker.js and imports the src/service-worker.js module, and creates a virtual $service-worker module that includes all the usual exports. build and prerendered are empty arrays.

I haven't added tests for this because I'm not really sure what they should look like.

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[AlbertMarashi]

@Rich-Harris @dummdidumm I believe firefox does not support imports inside of service workers, and this is creating errors during development in firefox. Any idea what we should do?

[dummdidumm]

As stated in the documentation, this needs support from the browser, so you'd need to use Chromium-based browsers during dev to test this. The alternative is to build and check the result in Preview mode.