Docs do not always clearly distinguish between import vs distribution packages

[CAM-Gerlach]

As discussed on the Python Discourse, the Using importlib_metadata documentation and its CPython equivalent do not always clearly distinguish between import packages and distribution packages, leading to user confusion.

Therefore, these terms should be clarified, used consistently (avoiding the ambiguous unqualified "package") and linked to their PyPA glossary entries. Furthermore, an admonition specifically calling this out and suggesting users use package_distributions() to map between them would be helpful.