Nodes: avoid slow and unecessary node group updates on file read

On file read we need to update group nodes in case the group they refer to
has changed its inputs and outputs. This had O(n^2) time complexity and was
updating all datablocks even if they did not change.

source/blender/nodes/texture/nodes/node_texture_common.c

@@ -174,7 +174,7 @@ void register_node_type_tex_group(void)
   node_type_socket_templates(&ntype, NULL, NULL);
   node_type_size(&ntype, 140, 60, 400);
   node_type_label(&ntype, node_group_label);
-  node_type_update(&ntype, NULL, node_group_verify);
+  node_type_group_update(&ntype, node_group_update);
   node_type_exec(&ntype, group_initexec, group_freeexec, group_execute);
 
   nodeRegisterType(&ntype);