Merged node UI: Renaming a merged node input or output does not have an effect on the labels in the subgraph view

Renaming a merged node input or output does not have an effect on the labels in the subgraph view.

To reproduce:

* Create two nodes (for example two Vector / Add)
* Select both
* Click Merge Selected Nodes
* Enter Subgraph
* Try renaming Inputs / Output from `Import Index N` to something else (Like `Dimention`)

Expected:

The names change in the UI

Actual:

The names stay as `Import Index N`

Examples:

View outside the subgraph after rename:

View inside the subgraph after rename:

Reproduce the issue by merging two nodes, entering the subgraph, and renaming an input or output from “Import Index N.” Trace the merged-node UI path that supplies labels to the subgraph view; done means the renamed labels update inside the subgraph as they do outside it.

索引モデルが issue の本文から書いたものです。