Web Worker support for Dojo 2 Applications

Dojo 2 Applications should support the use of Web Workers where they are available with some sort of fallback to ensure the application is still isomorphic.

The `worker-loader` allow with a call to `require(worker-loader?....)`, but we want to avoid inline usage of loaders.

Kit:

> Also, if we do go with an approach like this, we should still find a better way to integrate it. We _can_ type plugins now with something like:

```ts
declare module 'worker-loader?*' {
export = /* ... */
}
```

>Would we not be able to create something that wrapped ES `import()` that we could also inject some feature detection, so the code was isomorphic on Node.js as well?