bpo-44246: Update What's New for importlib.metadata. (#26408)

* bpo-44246: Update What's New for importlib.metadata.

Bump version of importlib_metadata included.
Add note about compatibility notice and fix link to entry_points documentation.
Add note about removal of access by index on Distribution.entry_points.

* Fix syntax mistake in issue reference.

Co-authored-by: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>

* Fix broken reference in entry-points.

Co-authored-by: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>