Meta issue for cleaning up import system cruft

@brettcannon

This is a meta issue tracking all the things that need to be cleaned up in the import system. From removing long deprecated APIs to migrating internal access to __spec__, we'll have several task lists for each related set of clean ups.

@brettcannon @ericsnowcurrently for visibility.

Removing deprecated APIs

Over in What's New for Python 3.11 there's a long list of things that have been deprecated long enough that they can be removed in Python 3.12. Here's that task list for tracking purposes. Watch for linked PRs (maybe one big one or many small ones -- we'll see!).

@brettcannon @ericsnowcurrently for visibility.

Update docs

Make sure examples and details from PEP 302 are covered in the importlib docs (/cc @Yhg1s )
Remove https://docs.python.org/3/reference/import.html#open-issues (PR)
It would be really nice to have a diagram.
(import_machinery.rst) how about a section devoted just to the attributes of modules and packages, perhaps expanding upon or supplanting the related entries in the data model reference page?
runpy, pkgutil, et al in the library manual should all get “See Also” links at the top pointing to the new import system section.
Add more explanation regarding the different ways in which __main__ is initialized?
Add more info on __main__ quirks/pitfalls (i.e. copy from PEP 395).