gh-120492: Sync importlib_metadata 8.2.0 (#124033)

* Sync with importlib_metadata 8.2.0

Removes deprecated behaviors, including support for `PackageMetadata.__getitem__` returning None for missing keys and Distribution subclasses not implementing abstract methods.
Prioritizes valid dists to invalid dists when retrieving by name (python/cpython/#120492). Adds SimplePath to `importlib.metadata.__all__`.

* Add blurb