[issue43720] Document various preexisting stdlib deprecations related to import for removal in Python 3.12

[Brett Cannon]

Change by Brett Cannon <brett at python.org>:


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keywords: +patch
pull_requests: +23908
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/25167

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue43720>
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