The lookupstring function for node sockets and node tree interface items was using the identifier strings of bNodeSocket. This would ensure uniqueness, but doesn't work nicely because the identifier is
not the RNA name property and differs for node groups (with regular nodes it only differs if socket names are duplicate).
Now removed the specialized callbacks, so that inputs/outputs collections simply use the name property. In cases where socket names are duplicate (e.g. math node "Value" + "Value") only the first socket
is returned, but in such cases access by index is the preferred method anyway.
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