GeezerVison

…`` in the data model (pythonGH-29389)

The documentation explaining Python's data model does not adequately explain
the differences between ``__getitem__`` and ``__class_getitem__``, nor does it
explain when each is called. There is an attempt at explaining
``__class_getitem__`` in the documentation for ``GenericAlias`` objects, but
this does not give sufficient clarity into how the method works. Moreover, it
is the wrong place for that information to be found; the explanation of
``__class_getitem__`` should be in the documentation explaining the data model.

This PR has been split off from pythonGH-29335.
(cherry picked from commit 31b3a70)

Co-authored-by: Alex Waygood <[email protected]>