(2.7) Upgrade type detection of `Option` to use `ReferenceType`

[cowtowncoder]

One improvement added in 2.7 (or partially in 2.6) regarding referential types is that type system now has special type, ReferenceType, which allows core databind to do some of handling that is specific to referential types. This can both simplify handling by modules (JDK8 and Guava modules have their own Optionals), and to let databind do some more advanced handling for things like @JsonValue.

Looking at existing handling, looks like Option is handled as a CollectionLikeType. This made some sense (since it is a container of 0 or 1 value(s)) earlier (to retain type parameter), but can now be improved. Looking at Scala code I have some idea how it might work, but just in case, here's how Guava module handles it:

public class GuavaTypeModifier extends TypeModifier
{
    @Override
    public JavaType modifyType(JavaType type, Type jdkType, TypeBindings bindings, TypeFactory typeFactory)
    {
        if (type.isReferenceType() || type.isContainerType()) {
            return type;
        }
        final Class<?> raw = type.getRawClass();
        if (raw == Optional.class) {
            return ReferenceType.upgradeFrom(type, type.containedTypeOrUnknown(0));
        }
        return type;
    }
}

and as far as I can see, it'd just need to change Optional.class to Scala equivalent Option and should work fine.

[cowtowncoder]

@nbauernfeind I mentioned this earlier, but didn't follow up. In addition to adding TypeModifier part, I think OptionDeserializerModule and OptionSerializerModule need minor change as type is no longer CollectionLikeType but ReferenceType.

In addition I am not sure there is need for OptionPropertyWriter any more: inclusion checks should (after change to use ReferenceType) work with handling by jackson-databind itself. This might even fix some bugs, although there is some risk of Scala module's handling differing from standard one (and if so, we wouldn't necessarily want default one).

Anyway, I think this change would be really good since I hope to further unify and simplify handling of these types: ideally modules would only indicate basic class (like Option) and the rest would be handled without modules' help.