The remove private _Py_UniversalNewlineFgetsWithSize() function from
the public C API: move it the internal C API (pycore_fileutils.h).
No longer export the function.
Move the private _PyLong converter functions to the internal C API
* _PyLong_FileDescriptor_Converter(): moved to pycore_fileutils.h
* _PyLong_Size_t_Converter(): moved to pycore_long.h
Argument Clinic now emits includes for pycore_fileutils.h and
pycore_long.h when these functions are used.