BaseScope.nestedScopesNotSymbols is not exposed

In C#, to add a new namespace scope, I need to check currentScope if that already existed, but this **nestedScopesNotSymbols** is not exposed to me, we do have **getNestedScopes** but I don't want that, I just need to check one level.

Related, instead of ```List```, (in C# would be ```IList```), would it better to be ```IReadonlyList```? And if the list could grow big (guess only in theory), ```IReadonlyDictionary``` can be faster to query on?

Best regards,

Start by locating BaseScope and the nestedScopesNotSymbols and getNestedScopes entry points. Compare the requested one-level access with the proposed read-only list or dictionary APIs; done means the chosen public API supports checking immediate namespace scopes and has coverage for its behavior.

Written by the indexing model from the issue text.