We already removed it from the online docs with #35132.
Currently it can only be "Built-In Types" (Variant types) or "Core"
(everything else), which is of limited use.
We might also want to consider dropping it from `ClassDB` altogether
in Godot 4.0.
This makes a VisualScriptEditor singleton, which gives plugins the
ability to register their own custom nodes. Those will be available for
insertion in the Visual Script editor, under the "Custom Nodes"
category.
