Restore removed private C API functions, macros and structures which have no
simple replacement for now:

* _PyDict_GetItem_KnownHash()
* _PyDict_NewPresized()
* _PyHASH_BITS
* _PyHASH_IMAG
* _PyHASH_INF
* _PyHASH_MODULUS
* _PyHASH_MULTIPLIER
* _PyLong_Copy()
* _PyLong_FromDigits()
* _PyLong_New()
* _PyLong_Sign()
* _PyObject_CallMethodId()
* _PyObject_CallMethodNoArgs()
* _PyObject_CallMethodOneArg()
* _PyObject_CallOneArg()
* _PyObject_EXTRA_INIT
* _PyObject_FastCallDict()
* _PyObject_GetAttrId()
* _PyObject_Vectorcall()
* _PyObject_VectorcallMethod()
* _PyStack_AsDict()
* _PyThread_CurrentFrames()
* _PyUnicodeWriter structure
* _PyUnicodeWriter_Dealloc()
* _PyUnicodeWriter_Finish()
* _PyUnicodeWriter_Init()
* _PyUnicodeWriter_Prepare()
* _PyUnicodeWriter_PrepareKind()
* _PyUnicodeWriter_WriteASCIIString()
* _PyUnicodeWriter_WriteChar()
* _PyUnicodeWriter_WriteLatin1String()
* _PyUnicodeWriter_WriteStr()
* _PyUnicodeWriter_WriteSubstring()
* _PyUnicode_AsString()
* _PyUnicode_FromId()
* _PyVectorcall_Function()
* _Py_IDENTIFIER()
* _Py_c_abs()
* _Py_c_diff()
* _Py_c_neg()
* _Py_c_pow()
* _Py_c_prod()
* _Py_c_quot()
* _Py_c_sum()
* _Py_static_string()
* _Py_static_string_init()

Patch by Victor Stinner.