[issue27938] PyUnicode_AsEncodedString, PyUnicode_Decode: add fast-path for "us-ascii" encoding

[Roundup Robot]

Change by Roundup Robot <devnull at psf.upfronthosting.co.za>:


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pull_requests: +4777

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue27938>
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