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

diff --git a/Doc/c-api/unicode.rst b/Doc/c-api/unicode.rst
index 5518214..54bd0a3 100644
--- a/Doc/c-api/unicode.rst
+++ b/Doc/c-api/unicode.rst
@@ -1098,6 +1098,9 @@
    .. versionchanged:: 3.7
       The return type is now ``const char *`` rather of ``char *``.
 
+   .. versionchanged:: 3.10
+      This function is a part of the :ref:`limited API <stable>`.
+
 
 .. c:function:: const char* PyUnicode_AsUTF8(PyObject *unicode)
 
diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst
index 738ef97..f57e1b4 100644
--- a/Doc/whatsnew/3.10.rst
+++ b/Doc/whatsnew/3.10.rst
@@ -323,6 +323,10 @@
   sending value into iterator without raising ``StopIteration`` exception.
   (Contributed by Vladimir Matveev in :issue:`41756`.)
 
+* Added :c:func:`PyUnicode_AsUTF8AndSize` to the limited C API.
+  (Contributed by Alex Gaynor in :issue:`41784`.)
+
+
 Porting to Python 3.10
 ----------------------