bpo-42085: Introduce dedicated entry in PyAsyncMethods for sending values (#22780)

diff --git a/Include/cpython/object.h b/Include/cpython/object.h
index 0db53c3..ec6a364 100644
--- a/Include/cpython/object.h
+++ b/Include/cpython/object.h
@@ -167,10 +167,13 @@ typedef struct {
     objobjargproc mp_ass_subscript;
 } PyMappingMethods;
 
+typedef PySendResult (*sendfunc)(PyObject *iter, PyObject *value, PyObject **result);
+
 typedef struct {
     unaryfunc am_await;
     unaryfunc am_aiter;
     unaryfunc am_anext;
+    sendfunc am_send;
 } PyAsyncMethods;
 
 typedef struct {