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

blank_issues_enabled: true
contact_links:
  - name: Ask a Question
    url: https://github.com/pyodide/pyodide/discussions
    about: Ask and answer Pyodide related questions
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    url: https://gitter.im/pyodide/community
    about: Chat with Pyodide community

blank_issues_enabled: true
contact_links:
  - name: Ask a Question
    url: https://github.com/pyodide/pyodide/discussions
    about: Ask and answer Pyodide related questions
  - name: 💬 Gitter
    url: https://gitter.im/pyodide/community
    about: Chat with Pyodide community
