bpo-42294: Add borrowed/strong reference to doc glossary (GH-23206)

Add "borrowed reference" and "strong reference" to the documentation
glossary.

Enhance also Py_INCREF() and Py_NewRef() documentation.
diff --git a/Doc/c-api/structures.rst b/Doc/c-api/structures.rst
index a9e1c6f..03fe479 100644
--- a/Doc/c-api/structures.rst
+++ b/Doc/c-api/structures.rst
@@ -66,7 +66,7 @@
 
    Get the type of the Python object *o*.
 
-   Return a borrowed reference.
+   Return a :term:`borrowed reference`.
 
    .. versionchanged:: 3.10
       :c:func:`Py_TYPE()` is changed to the inline static function.