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

package:
  name: svgwrite
  version: 1.4.3
  top-level:
    - svgwrite
source:
  url: https://files.pythonhosted.org/packages/84/15/640e399579024a6875918839454025bb1d5f850bb70d96a11eabb644d11c/svgwrite-1.4.3-py3-none-any.whl
  sha256: bb6b2b5450f1edbfa597d924f9ac2dd099e625562e492021d7dd614f65f8a22d
about:
  home: http://github.com/mozman/svgwrite.git
  PyPI: https://pypi.org/project/svgwrite
  summary: A Python library to create SVG drawings.
  license: MIT License

package:
  name: svgwrite
  version: 1.4.3
  top-level:
    - svgwrite
source:
  url: https://files.pythonhosted.org/packages/84/15/640e399579024a6875918839454025bb1d5f850bb70d96a11eabb644d11c/svgwrite-1.4.3-py3-none-any.whl
  sha256: bb6b2b5450f1edbfa597d924f9ac2dd099e625562e492021d7dd614f65f8a22d
about:
  home: http://github.com/mozman/svgwrite.git
  PyPI: https://pypi.org/project/svgwrite
  summary: A Python library to create SVG drawings.
  license: MIT License
