[C API] Add PyDict_NewPresized() function #139772

There is a private _PyDict_NewPresized() function which is used by 11 projects of the PyPI top 15,000 projects:

• Nuitka (2.7.16)
• cython (3.1.4)
• frozendict (2.4.6)
• gevent (25.9.1)
• mercurial (7.1.1)
• mypy (1.18.2)
• mypy_dev-1.19.0a2
• numba (0.62.0)
• orjson (3.11.3)
• ormsgpack (1.10.0)
• serpyco_rs (1.17.1)

I propose to make the function public.

Linked PRs

• gh-139772: Add PyDict_NewPresized() function #139773
• gh-139772: Add PyDict_FromItems() function #139963
• gh-139772: Add PyDict_FromKeysAndValues() function #141682