Sync with importlib_metadata for Python 3.16 #160386

Tracking issue for applying importlib_metadata changes to importlib.metadata in 3.16, continuing the pattern of #132947 (3.15) and #117089 (3.13).

This covers importlib_metadata 9.0.1 and 9.1.0:

• Prefer the greater metadata directory when a path supplies more than one. Children are now considered in reverse lexicographic order, so stale metadata left behind by an interrupted or unclean upgrade no longer shadows the version in use (Invalid metadata directory leads to errors #100666).
• Identify the distribution when a required metadata field is missing. Distribution.name and .version now raise a KeyError naming both the field and the distribution, and PathDistribution renders itself as its metadata path.
• Defer EntryPoint.value validation until use. Construction no longer validates, so one malformed entry point no longer prevents entry points in other groups from being selected (Using entry-point value for non-object references importlib_metadata#523).
• importlib.metadata.diagnose no longer crashes on a metadata directory with no metadata file, or whose metadata declares no name; such distributions are reported by their location (Diagnose crashes on empty metadata directory importlib_metadata#548).
• SimplePath.joinpath and SimplePath.__truediv__ take other positional-only, so pathlib.Path satisfies the protocol under type checkers that compare parameter names (SimplePath rejects pathlib.Path: joinpath and __truediv__ are not positional-only importlib_metadata#542).

Two further items that are cleanups rather than behavior changes:

• Prepared.normalize returns to the re.sub implementation. The hand-rolled version from importlib.metadata: Use str.translate to improve performance of importlib.metadata.Prepared.normalized #143658 was reverted upstream, so keeping it here would be fresh drift.
• Lib/importlib/metadata/_typing.py is removed along with its import. Its only export, md_none, lost its last call site when Distribution.metadata began raising MetadataNotFound (Regression: importlib.metadata.PathDistribution.requires raises AttributeError, name/version raises TypeError #143387), but the import line survived the merge that landed that change, leaving an unused module imported by nothing.

Linked PRs

• gh-160386: Apply changes from importlib_metadata 9.1 #160387