Improve importlib backports-upstream integration

The current status-quo when it comes to the development integration/synchronization between the importlib backports and the CPython upstream isn't optimal.

Before anything else, I must properly acknowledge @jaraco's monumental and tireless effort on maintaining the importlib backports, and handling the complex synchronization with the CPython upstream, not to mention the continued development of these modules. It has been instrumental to get things to the state they are today, and none of the issues discussed in this thread should reflect negatively on him, but rather our failure to ensure these projects got the resources they need — a far too common tale in open-source.

Here are some issues I think we should improve:

• Synchronization process — even though @jaraco has left comments in some PRs describing his workflow, there's no properly documented process
• Authorship stripping — the current way changes are synced in and from the backports strip commit authorship
• Documentation fragmentation, resulting in a sub-optimal documentation
  • Eg. importlib.metadata.Distribution, and other classes, do not document their attributes (I regularly have to resort to the source code)
• CLA enforcement — the backports do not enforce the CLA
• Segmented development workflow — issues and changes happen in both places
• Source history — the current way changes are synced in and from the backports strip commit history

cc @python/importlib-team

この issue ではファイルもテストも指定されていません。まず importlib backports と CPython upstream synchronization workflow を確認し、著作者情報、ソース履歴、CLA の適用、ドキュメントに関する懸念事項を含めて検討してください。完了とみなすには、統合プロセスについて合意された改善が必要ですが、この issue では具体的な実装も受け入れ基準も定義されていません。