bpo-41784: make PyUnicode_AsUTF8AndSize part of the limited API (GH-22252)

diff --git a/Include/cpython/unicodeobject.h b/Include/cpython/unicodeobject.h
index 300408c..f1b4455 100644
--- a/Include/cpython/unicodeobject.h
+++ b/Include/cpython/unicodeobject.h
@@ -727,26 +727,6 @@ PyAPI_FUNC(int) _PyUnicode_FormatAdvancedWriter(
 /* --- Manage the default encoding ---------------------------------------- */
 
 /* Returns a pointer to the default encoding (UTF-8) of the
-   Unicode object unicode and the size of the encoded representation
-   in bytes stored in *size.
-
-   In case of an error, no *size is set.
-
-   This function caches the UTF-8 encoded string in the unicodeobject
-   and subsequent calls will return the same string.  The memory is released
-   when the unicodeobject is deallocated.
-
-   _PyUnicode_AsStringAndSize is a #define for PyUnicode_AsUTF8AndSize to
-   support the previous internal function with the same behaviour.
-*/
-
-PyAPI_FUNC(const char *) PyUnicode_AsUTF8AndSize(
-    PyObject *unicode,
-    Py_ssize_t *size);
-
-#define _PyUnicode_AsStringAndSize PyUnicode_AsUTF8AndSize
-
-/* Returns a pointer to the default encoding (UTF-8) of the
    Unicode object unicode.
 
    Like PyUnicode_AsUTF8AndSize(), this also caches the UTF-8 representation
diff --git a/Include/unicodeobject.h b/Include/unicodeobject.h
index 90b3299..b0ac086 100644
--- a/Include/unicodeobject.h
+++ b/Include/unicodeobject.h
@@ -468,6 +468,23 @@ PyAPI_FUNC(PyObject*) PyUnicode_AsUTF8String(
     PyObject *unicode           /* Unicode object */
     );
 
+/* Returns a pointer to the default encoding (UTF-8) of the
+   Unicode object unicode and the size of the encoded representation
+   in bytes stored in *size.
+
+   In case of an error, no *size is set.
+
+   This function caches the UTF-8 encoded string in the unicodeobject
+   and subsequent calls will return the same string.  The memory is released
+   when the unicodeobject is deallocated.
+*/
+
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030A0000
+PyAPI_FUNC(const char *) PyUnicode_AsUTF8AndSize(
+    PyObject *unicode,
+    Py_ssize_t *size);
+#endif
+
 /* --- UTF-32 Codecs ------------------------------------------------------ */
 
 /* Decodes length bytes from a UTF-32 encoded buffer string and returns