Cast in `ScopeGraphUtils`

[AZWN]

Short description
Remove cast in ScopeGraphUtils.

Problem description.
In order to keep Java 11 type inference happy, an cast was inserted in

nabl/scopegraph/src/main/java/mb/scopegraph/oopsla20/ScopeGraphUtil.java

Line 23 in 3ee894a

t -> (Map.Entry<L, Iterable<S>>)new AbstractMap.SimpleImmutableEntry<L, Iterable<S>>(t.getKey().getValue(), t.getValue()), Collectors.toSet())));

Describe the solution you'd like
It would be better to fin the correct type bounds, and add those explicitly

Describe alternatives you've considered

Additional context
Not having the cast works in Java 8