Use federated modules in workers

### Problem

The workers currently don't participate in module federation, so they get key upstream kernel-level packages fixed at build time, e.g. `@jupyterlite/contents`. This makes it hard to test PRs on `jupyterlite`, and result in a few hundred extra kb on disk when loaded.

### Proposed Solution

Figure out how to change the webpack configuration to make these workers consume upstream

### Additional context

Some related comments:
- https://github.com/jupyterlite/jupyterlite/pull/1723#issuecomment-3271514184