Links created through the normal Python API are invalid since
7026096099. Before then, one could create links to or from virtual
sockets from Python (grayed out sockets in Group Input and Group
Output nodes), as is still possible in the GUI.
This is documented as an API change, and it broke at least Node
Wrangler, see #104470. Instead of just fixing that, let's introduce an
API to make this operation simpler.
Damien Picard