[refactor] add tree parent node mergeCell demo and add api needed

[fangsmile]

[fangsmile]

row or col should get from tableInstance

 customMergeCell: (col, row, table) => {
    if (col >=0 && col <=5 && row==2) {
      return {
        text: table.getCellValue(0,2),
        range: {
          start: {
            col: 0,
            row: 2
          },
          end: {
            col: 5,
            row: 2
          }
        },
        // style: {
        //   bgColor: 'white'
        // }
      };
    }
  }

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[github-actions[bot]]

This issue has been automatically closed because it did not have recent activity. If this remains to be a problem with the latest version of @VisActor/vtable, please open a new issue and link this to it. Thanks!