feat(legend): Provide original data id in format callback

[netil]

Issue

#3663

Details

When data.names option is specified, provide original data id to format callback

bb.generate({
  data: {
    names: {
      "data1": "Detailed Name",
      "data2": "Name Detailed"
    },
    columns: [
      ["data1", 71.4],
      ["data2", 10],
    ],
    type: "gauge"
  },
  legend: {
    format(id, dataId) {
       return id === "Name Detailed" ? dataId : id;
    },
    tooltip: true
  }
});

[coveralls]

coverage: 94.263% (+0.001%) from 94.262%
when pulling 280cafa on netil:legend#3663
into 0c9fbc6 on naver:master.