Create a function on CurvesGeometry that can also be used for an edit mode operator in the future. Dealing with CustomData directly means the code is a bit more verbose than would be ideal, but this would be a simple thing to clean up in the future if we get an attribute API here. Also change the reverse node to first work on a read-only geometry component, and only get write access if there is a curve selected. Differential Revision: https://developer.blender.org/D14375