Add support for buildPython version 3.12

[mhsmith]

Checklist in product/gradle-plugin/README.md.

For runtime support, see #967.

[mhsmith]

Critical bug: beeware/briefcase#1480

> Task :app:generateDebugPythonRequirements FAILED
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "C:\Users\user\github\beeware\briefcase\tmp\helloworld\build\helloworld\android\gradle\app\build\generated\python\bp\chaquopy\pip_install.py", line 23, in <module>
    from pip._internal.utils.misc import rmtree
  File "C:\Users\user\github\beeware\briefcase\tmp\helloworld\build\helloworld\android\gradle\app\build\generated\python\bp\pip\_internal\utils\misc.py", line 20, in <module>
    from pip._vendor import pkg_resources
  File "C:\Users\user\github\beeware\briefcase\tmp\helloworld\build\helloworld\android\gradle\app\build\generated\python\bp\pip\_vendor\pkg_resources\__init__.py", line 58, in <module>
    from pip._vendor.six.moves import urllib, map, filter
ModuleNotFoundError: No module named 'pip._vendor.six.moves'

[mhsmith]

The error from six in the Briefcase issue was fixed by updating six to a version that's compatible with Python 3.12.

The removal of distutils from the standard library was fixed by updating to the current version of setuptools. We had a few patches in pkg_resources/__init__.py, but I've removed them because it looks like they were connected to putting build-packages.zip directly on the PYTHONPATH, which we don't do anymore. This means we no longer have any patches against upstream setuptools.

[mhsmith]

Finally, in order for the setuptools .pth file with the distutils redirection to take effect, we had to stop running pip using python -S, and use a proper virtual environment instead. (This code was originally written for Python 2, which didn't have virtual environment support in the standard library.)