docs: private IonWriter build(_Private_FastAppendable appender)
      {
          IonCatalog catalog = getCatalog();
          SymbolTable[] imports = getImports();
  
          // TODO We shouldn't need a system here
          IonSystem system =
              IonSystemBuilder.standard().withCatalog(catalog).build();
  
          SymbolTable defaultSystemSymtab = system.getSystemSymbolTable();
  
          IonWriterSystemText systemWriter =
              (getCallbackBuilder() == null
                  ? new IonWriterSystemText(defaultSystemSymtab,
                                            this,
                                            appender)
                  : new IonWriterSystemTextMarkup(defaultSystemSymtab,
                                                  this,
                                                  appender));
  
          SymbolTable initialSymtab =
              initialSymtab(((_Private_ValueFactory)system).getLstFactory(), defaultSystemSymtab, imports);
  
          return new IonWriterUser(catalog, system, systemWriter, initialSymtab);
      }