Previously the edge index was always determined by the field context, and the node didn't work when the context was in any other domain. Adding an index input makes it work much more nicely with the other topology nodes. It's now in the topology submenu too. I also reimplemented the edge positions input to use the field at index node internally. That will probably make it slower for now, but we need to optimize that to do nothing in some special cases anyway. Differential Revision: https://developer.blender.org/D16105