Types for the PAO extension. The type system `PaoTypeSystem` adds several new methods for boxing and unboxing primitive values. Also, new implementations of {@link polyglot.types.ParsedClassType polyglot.types.ParsedClassType} and {@link polyglot.types.PrimitiveType polyglot.types.PrimitiveType} are provided, to implement the functionality that primitive types are now regarded as extending `Object`.