[issue42141] Speedup various dict inits

[Inada Naoki]

Inada Naoki <songofacandy at gmail.com> added the comment:

> 1. dicts from other dicts that are not "perfect" (combined and without holes)
> 3. copies of dicts with many holes

Note that I have optimized and rejected it by myself already.
See https://github.com/python/cpython/pull/21669
and https://bugs.python.org/issue41431#msg374556

Code duplication is too huge compared to performance gain.

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nosy: +methane

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