scriptURL of serviceWorker.register isn't considered part of bundle

👋🏼

I'm currently working with microbundle to package a service worker library. I have a file [`index.mjs`](https://github.com/TimDaub/web3-service-worker-cache/blob/demo/src/index.mjs) that takes care of initializing and handling the SW in the main thread. And I have a file [`worker.mjs`](https://github.com/TimDaub/web3-service-worker-cache/blob/demo/src/worker.mjs) that separates the service worker code.

After browser compatability, I register the worker like this:

```js
await navigator.serviceWorker.register('./worker.mjs');
```

I use `microbundle` in a standard way by configuring it in [package.json](https://github.com/TimDaub/web3-service-worker-cache/blob/demo/package.json).

I'm aware that no bundler would take the input of `register(scriptURI)` and make it somehow part of the output. Usually, a developer has to care for this separately e.g. in rollup by adding a secondary input and output. But today while doing that I found it annoying and I asked myself why?

Couldn't microbundle just take care of transpiling the worker.mjs file and include it somehow? E.g. it could be bundled as a base64 data URI...