[Bug] dimension tooltip 一个 datum 在多个 band 轴下出现多行 tooltip 内容项

[zamhown]

复现 spec：

const spec = {
  type: 'common',
  data: {
    values: [
      {
        time: '2:00',
        value: 8
      },
      {
        time: '4:00',
        value: 9
      },
      {
        time: '6:00',
        value: 11
      },
      {
        time: '8:00',
        value: 14
      },
      {
        time: '10:00',
        value: 16
      },
      {
        time: '12:00',
        value: 17
      },
      {
        time: '14:00',
        value: 17
      },
      {
        time: '16:00',
        value: 16
      },
      {
        time: '18:00',
        value: 15
      }
    ]
  },
  series: [{
    type: 'line',
    xField: 'time',
    yField: 'value'
  }],
  axes: [
    { type: 'band', orient: 'top' },
    { type: 'band', orient: 'bottom' },
    { type: 'linear', orient: 'left' },
  ]
};

const vchart = new VChart(spec, { dom: CONTAINER_ID });
vchart.renderAsync();

// Just for the convenience of console debugging, DO NOT COPY!
window['vchart'] = vchart;