Animation: send notifier when keyframe is inserted

`<some_id>.keyframe_insert()` now sends a notifier that animation data
was changed, so that animation-related editors can properly refresh.

Since this function is quite high-level (if necessary it creates the
Action and FCurves), I thought this would be a suitable location for the
notifier. If high keyframing speed is required, it is still recommended
to use `FCurveKeyframePoints.insert(options={'FAST'})` instead.

source/blender/python/intern/bpy_rna_anim.c

@@ -401,6 +401,10 @@ PyObject *pyrna_struct_keyframe_insert(BPy_StructRNA *self, PyObject *args, PyOb
     return NULL;
   }
 
+  if (result) {
+    WM_event_add_notifier(C, NC_ANIMATION | ND_ANIMCHAN | NA_EDITED, NULL);
+  }
+
   return PyBool_FromLong(result);
 }