Fix generator bug with non-public nested types (#374)

Author: jasongin

src/NodeApi.Generator/ModuleGenerator.cs

@@ -475,7 +475,8 @@ private void ExportType(
             $"{nameof(JSPropertyAttributes)}.{nameof(JSPropertyAttributes.Enumerable)}";
 
         // Declare nested types first, so they can be exported as static properties of this type.
-        foreach (INamedTypeSymbol nestedType in type.GetTypeMembers())
+        foreach (INamedTypeSymbol nestedType in type.GetTypeMembers()
+            .Where((t) => t.DeclaredAccessibility == Accessibility.Public))
         {
             ExportType(ref s, nestedType, GetExportName(nestedType));
         }

test/TestCases/napi-dotnet/ComplexTypes.cs

@@ -199,6 +199,11 @@ public NestedClass(string value)
 
         public string Value { get; set; }
     }
+
+    // Non-public nested types should not be exported.
+    internal class PrivateNestedClass
+    {
+    }
 }
 
 [JSExport]