gh-100238: Vendor distutils for peg_generator by lysnikolaou · Pull Request #104744 · python/cpython

Is there a reason we can't use setuptools via pip install rather than bringing back all this code we just removed?

Not really. I opened this in a hurry to give @Yhg1s the option to unskip test_peg_generator before beta1, since the associated issue was marked as a release blocker. Since the consensus is that it's not, I'll take the time to port this to setuptools instead.