[issue32337] Dict order is now guaranteed, so add tests and doc for it

[Serhiy Storchaka]

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


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nosy: +ned.deily
priority: normal -> release blocker

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32337>
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