pipx does not find dependencies from extras

[itsayellow]

Describe the bug

pipx accurately installs from a package spec with extras, but it does not keep track of the dependencies from extras in its metadata.

Consequently, using the argument --include-deps with install will not install the apps of the dependencies from extras.

The problem is that we only supply the name of the main package to venv_metadata_inspector.py and not its extras.

Is there a way to determine the extras used to install a package from the venv? I was unable to find any.

How to reproduce

> pipx install 'nox[tox_to_nox]' --include-deps
⚠️  Note: register-python-argcomplete was already on your PATH at /usr/local/bin/register-python-argcomplete
  installed package nox 2020.8.22, Python 3.9.0
  These apps are now globally available
    - activate-global-python-argcomplete
    - nox
    - python-argcomplete-check-easy-install-script
    - python-argcomplete-tcsh
    - register-python-argcomplete
    - tox-to-nox
    - virtualenv
done! ✨ 🌟 ✨

Expected behavior

Since tox is installed to the venv with extra tox_to_nox, the app tox should have been exposed.

Also, viewing pipx_metadata.json in the nox venv shows no mention of the extra packages in app_paths_of_dependencies or apps_of_dependencies.