[issue43224] Add support for PEP 646

[Serhiy Storchaka]

Change by Serhiy Storchaka <storchaka+cpython at gmail.com>:


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pull_requests: +29925
pull_request: https://github.com/python/cpython/pull/31828

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue43224>
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