bpo-42382: In importlib.metadata, `EntryPoint` objects now expose `dist` (#23758)

* bpo-42382: In importlib.metadata, `EntryPoint` objects now expose a `.dist` object referencing the `Distribution` when constructed from a `Distribution`.

Also, sync importlib_metadata 3.3:

- Add support for package discovery under package normalization rules.
- The object returned by `metadata()` now has a formally-defined protocol called `PackageMetadata` with declared support for the `.get_all()` method.

* Add blurb

* Remove latent footnote.