[docs] [issue18578] Rename and document test.bytecode_helper as test.support.bytecode_helper

[Joannah Nanjekye]

Change by Joannah Nanjekye <nanjekyejoannah at gmail.com>:


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pull_requests: +14900
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/15168

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue18578>
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