Group Node convert to input isn't preserved when converting back to nodes.

To reproduce:

- Create a group node from a collection of nodes
- Convert one of the widgets on the group node to an input
- Convert the group node back to a collection of nodes

Expected result: the widget that was converted to an input is now an input on the separate node

Observed result: the widget that had been converted to an input has been converted back to a widget

The newly created input does operate correctly as an input for the group node, it's just lost when converting back to nodes.