Geometry Nodes: automatically reconnect when swapping inputs

This makes it easier to swap the inputs to the Join Geometry node.
The behavior is the same as in the Math node.

source/blender/nodes/function/node_function_util.cc

@@ -28,4 +28,5 @@ void fn_node_type_base(bNodeType *ntype, int type, const char *name, short nclas
   node_type_base(ntype, type, name, nclass, flag);
   ntype->poll = fn_node_poll_default;
   ntype->update_internal_links = node_update_internal_links_default;
+  ntype->insert_link = node_insert_link_default;
 }