py-setuptools: install setuptools from wheels directly (#31131)

When installing setuptools from sources in Spack, we might
get into weird failures due to the way we use pip.

In particular, for Spack it's necessary to install in a
non-isolated pip environment to allow using PYTHONPATH as a
selection method for all the build requirements of a
Python package.

This can fail when installing setuptools since there might
be a setuptools version already installed for the Python
interpreter being used, with different entry points than
the one we want to install.

Installing from wheels both pip and setuptools should
harden our installation procedure in the context of:
- Bootstrapping Python dependencies of Spack
- Using external Python packages

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