Add package_type field to repodata.json. ### Description

This PR adds `package_type` field to repodata.json and use it to create a list of unvendored standard libraries. After this we don't need to manage a hard-coded list of unvendored stdlib lists in pyodide-py.

### Checklists

- [x] Add / update tests

// This file is just needed to make "npx tsd" work (otherwise it will quit with an error).

// This file is just needed to make "npx tsd" work (otherwise it will quit with an error).
