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.

Lib/test/test_importlib/test_zip.py

@@ -3,8 +3,12 @@ import unittest
 
 from contextlib import ExitStack
 from importlib.metadata import (
-    distribution, entry_points, files, PackageNotFoundError,
-    version, distributions,
+    PackageNotFoundError,
+    distribution,
+    distributions,
+    entry_points,
+    files,
+    version,
 )
 from importlib import resources