Adopt build because running setup.py is deprecated for security reasons

[cclauss]

https://setuptools.pypa.io/en/latest/userguide/quickstart.html#setup-py

To avoid executing arbitrary scripts and boilerplate code, we are transitioning into a full-fledged setup.cfg to declare your package information instead of running setup().

See warning at https://setuptools.pypa.io/en/latest/deprecated/commands.html

running python setup.py directly as a script is considered deprecated. This also means that users should avoid running commands directly via python setup.py <command>.

% git grep setup\\.py

.github/workflows/python-publish.yml:      run: python setup.py build
.github/workflows/python-publish.yml:      run: python setup.py sdist bdist_wheel
CHANGELOG.rst:* Several minors updates to setup.py and tox
docs/release_process.rst:they lock the oauthlib version in ``setup.py`` and release anyway.
tox.ini:# as of today, RTD is using python3.7 and doesn't run "setup.py install"

https://pypa-build.readthedocs.io

Also, use https://pypi.org/project/setuptools-py2cfg to eliminate or greatly reduce setup.py. This could be a step towards using https://pypi.org/project/pyproject-migrator to get to replace setup.* with a pyproject.toml file.