[manifests] Vendor pathspec-py3 CIPD wheel

Mypy 2.0+ requires `pathspec >= 1.0.0` at runtime to support gitignore-
style file exclusion patterns. Because `pathspec` is not mirrored as a
git repository on `fuchsia.googlesource.com`, vendor the pure-Python
`infra/python/wheels/pathspec-py3` (`version:1.0.4`) wheel via CIPD:

- Update `manifests/prebuilts` and `manifests/jiri.lock` to fetch
  `infra/python/wheels/pathspec-py3` (`version:1.0.4`) into
  `prebuilt/third_party/pathspec-py3-wheel`.
- Add `tools/build/scripts/extract_pathspec_wheel.sh` and register the
  `install-pathspec-py3` Jiri hook in `manifests/platform` to extract
  the wheel into `prebuilt/third_party/pathspec-py3` and generate its
  `BUILD.gn` and `README.fuchsia`.
- Update `tools/check-licenses` configurations to skip the unextracted
  wheel directory (`prebuilt/third_party/pathspec-py3-wheel`) and allow
  the `MPL-2.0` license for the extracted host-only `pathspec-py3`
  package.

Bug: 489061889
Bug: 569952695
Change-Id: Idf80e8cffb328e3176773def3292b4a24f13fd24
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1858358
Commit-Queue: Nathaniel Manista <nathaniel@google.com>
Presubmit-Verified: fuchsia-internal-scoped@luci-project-accounts.iam.gserviceaccount.com <fuchsia-internal-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Clayton Wilkinson <wilkinsonclay@google.com>
Fuchsia-Auto-Submit: Nathaniel Manista <nathaniel@google.com>