bpo-39022, bpo-38594: Sync with importlib_metadata 1.3 (GH-17568)

* bpo-39022, bpo-38594: Sync with importlib_metadata 1.3 including improved docs for custom finders and better serialization support in EntryPoints.

* 📜🤖 Added by blurb_it.

* Correct module reference
4 files changed