docs: public static void setMetaClass(Object self, MetaClass metaClass) {
          if (metaClass instanceof HandleMetaClass)
              metaClass = ((HandleMetaClass)metaClass).getAdaptee();
  
          if (self instanceof Class) {
              GroovySystem.getMetaClassRegistry().setMetaClass((Class) self, metaClass);
          } else {
              ((MetaClassRegistryImpl)GroovySystem.getMetaClassRegistry()).setMetaClass(self, metaClass);
          }
      }