This change makes the Set Position node do nothing by default. The Position input is now hidden by default and is implicitly the position (similar to what we want to do in Noise nodes). The socket inspection also shows this already.
The implementation is very simple for now. Eventually, I want to integrate that with the socket declaration system (whereas a socket can specify what the default should be). However, before doing that I'd like to use the new node declaration system for geometry group nodes as well (so that this behavior can be properly exposed to the outside of a node group).