[issue37483] Add PyObject_CallOneArg()

[Inada Naoki]

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

> Macros cannot be used in all C extensions. For the PEP 587, I was asked to replace macros with functions.

This is just an helper inline function / macro to ease calling _PyObject_Vectorcall.
Extensions can port this helper inline function / macro to ease calling _PyObject_Vectorcall.

I don't want to make this non-inline function.

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