* nasgen generated maps are mostly used only with the current class (after recent class sharing changes). getInitialMap package-private accessors can be removed.
* GlobalObject was a way to shield classloader boundary (in the past jdk.nashorn.internal.objects.* were loaded by a different loader and hence runtime can't refer to Global class). This is not needed anymore. Also Context.getGlobal/setGlobal can use Global type and avoid Global/GlobalObject cast in many places.