This is a partial solution to the task T51604.
Only suports auto-smooth for Meshs (not Edit-Meshs)
A special attention must be paid to rdata->poly_normals. It may be better to use a CustomData than to allocate and release every time that the smoot_angle changes.
Other more efficient solutions could be:
- Update VBO only;
- Use the glBufferSubData to update just a subset of the object's buffer data;
Feel free to edit and/or commit the patch ;)