图例鼠标移动上去，如何给具体某一图例出现自定义提示

[jwlovelife]

plot.on('legend-item:mouseover', ev => {
const target = ev.target;
const delegateObject = target.get('delegateObject');
const item = delegateObject.item; // 图例选项
// 如何将获得图例item出现tooltip
});

Checklist

• npm test passes
• benchmarks are included
• commit message follows commit guidelines
• documents are updated

Description of change