function revive(state=initialState) {
  return {
    ...state,
    workbench: {
      ...state.workbench,
      initialCode: state.workbench.code,
      parserSettings: state.parserSettings[state.workbench.parser] || null,
      transform: {
        ...state.workbench.transform,
        initialCode: state.workbench.transform.code,
      },
    },
  };
}
When read from persistent storage, set the last stored code as initial version.
This is necessary because we use CodeMirror as an uncontrolled component.