Unmodifiable JDK9 collections not marshallable with ProtoStream

JDK9 introduced a number of new unmodifable collection classes:

• Empty implementations of java.util.Map, java.util.List, and java.util.Set.
  • As returned via List.of(), Set.of(), Map.of(), or Map.ofEntries()
  • N.B. These are different than the impls returned by Collections.emptyMap()/emptyList()/emptySet().
• Tiny implementations of java.util.Map, java.util.List, and java.util.Set.
  • As returned via List.of(...), Set.of(...), Map.of(...), or Map.ofEntries(...)
  • N.B. These are different that the impls returned by Collections.singletonMap(...)/singletonList(...)/singleton(...)
• Arbitrary-size implementations of java.util.Map, java.util.List, and java.util.Set.
  • As returned via Map.of(...), List.of(...), Set.of(...) with more than 2 parameters, or Map.ofEntries(...) with more than 1 parameter

These implementations are not currently marshallable with ProtoStream.