Add missing PyUnicode_GetDefaultEncoding function documentation

Author: rruuaanng

Doc/c-api/unicode.rst

@@ -612,6 +612,11 @@ APIs:
    decref'ing the returned objects.
 
 
+.. c:function:: const char* PyUnicode_GetDefaultEncoding(void)
+
+   Return the default encoding format of the string.
+
+
 .. c:function:: Py_ssize_t PyUnicode_GetLength(PyObject *unicode)
 
    Return the length of the Unicode object, in code points.

Doc/data/refcounts.dat

@@ -2750,6 +2750,9 @@ PyUnicode_FromFormatV:PyObject*::+1:
 PyUnicode_FromFormatV:const char*:format::
 PyUnicode_FromFormatV:va_list:args::
 
+PyUnicode_GetDefaultEncoding:const char*:::
+PyUnicode_GetDefaultEncoding::void::
+
 PyUnicode_GetLength:Py_ssize_t:::
 PyUnicode_GetLength:PyObject*:unicode:0: