[Feature] Support for accessibility of elements inside the chart (series, legend...)

### What problem does this feature solve?

I know echart has done a lot on accessibility, thanks a lot.

The purpose of this issue is want to know whether the Echart team has plans to support further improvement of the accessibility function, so that users can access specific elements inside the chart and operate them through tab, arrow keys and space keys.

### What does the proposed API look like?

This is just an idea, take pie chart as an example.

```javascript

const myChart = echarts.init(document.getElementById('main'), null, { renderer: 'svg' });

const option = {
aria: {
show: true
},
series: [
{
name: 'Referrer',
type: 'pie',
data: [
{ value: 335, name: 'Direct Visit', ariaLabel: 'aria label for Direct visit' },
{ value: 310, name: 'Email Marketing' , ariaLabel: 'aria label for Email Marketing' },
{ value: 234, name: 'Union Ad' },
]
}
]
};
myChart.setOption(option);

```