perform yield from delegation by repeating YIELD_FROM opcode (closes #14230)

This allows generators that are using yield from to be seen by debuggers. It
also kills the f_yieldfrom field on frame objects.

Patch mostly from Mark Shannon with a few tweaks by me.

Include/frameobject.h

@@ -27,7 +27,6 @@ typedef struct _frame {
        to the current stack top. */
     PyObject **f_stacktop;
     PyObject *f_trace;          /* Trace function */
-    PyObject *f_yieldfrom;      /* Iterator being delegated to by yield from */
 
         /* In a generator, we need to be able to swap between the exception
            state inside the generator and the exception state of the calling

Include/genobject.h

@@ -19,7 +19,7 @@ typedef struct {
 
     /* True if generator is being executed. */
     char gi_running;
-    
+
     /* The code object backing the generator */
     PyObject *gi_code;
 
@@ -35,6 +35,7 @@ PyAPI_DATA(PyTypeObject) PyGen_Type;
 PyAPI_FUNC(PyObject *) PyGen_New(struct _frame *);
 PyAPI_FUNC(int) PyGen_NeedsFinalizing(PyGenObject *);
 PyAPI_FUNC(int) PyGen_FetchStopIterationValue(PyObject **);
+PyObject *_PyGen_Send(PyGenObject *, PyObject *);
 
 #ifdef __cplusplus
 }