[roll] Roll fuchsia [superproject] Roll third_party/pigweed pw_build: Python script for the build_wheel target

This adds generate_python_wheel.py to replace the direct call to
python -m build within GN.

The behavior remains the same with two additions:

- Stale wheel files from old builds are deleted first
- After the wheel is created a 'requirements.txt' is written with the
  package name==version and the sha256 line. This will be used in a
  followup CL to install Python wheel artifacts with: `pip install
  --require-hashes`

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/153710
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Original-Revision: bd9a7eb032a379aa85174c2f8a1672ca06faf262
GitOrigin-RevId: db7bb09a1fb2e1b5db484323912cf2ba2cfc9c9c
Roller-URL: https://ci.chromium.org/b/8775897658994201793
CQ-Do-Not-Cancel-Tryjobs: true
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/882811
Original-Revision: b87062d2461e554d56f02e8f249ebdf69d675c56
Change-Id: I9a511bd6a49c85f5089818b13903294801f9a53b