docs: public final IonSystem build()
      {
          IonCatalog catalog =
              (myCatalog != null ? myCatalog : new SimpleCatalog());
  
          IonTextWriterBuilder twb =
              IonTextWriterBuilder.standard().withCharsetAscii();
          twb.setCatalog(catalog);
  
          _Private_IonBinaryWriterBuilder bwb =
              _Private_IonBinaryWriterBuilder.standard();
          bwb.setCatalog(catalog);
          bwb.setStreamCopyOptimized(myStreamCopyOptimized);
  
          // TODO Would be nice to remove this since it's implied by the BWB.
          //      However that currently causes problems in the IonSystem
          //      constructors (which get a null initialSymtab).
          SymbolTable systemSymtab = _Private_Utils.systemSymtab(1);
          bwb.setInitialSymbolTable(systemSymtab);
          // This is what we need, more or less.
  //        bwb = bwb.fillDefaults();
          IonReaderBuilder rb = IonReaderBuilder.standard().withCatalog(catalog);
          IonSystem sys = newLiteSystem(twb, bwb, rb);
  
          return sys;
      }