[Feature] brush 选框触发方式问题

### What problem does this feature solve?

目前echarts支持通过某个属性设置brush吗，现在的方式是需要有个工具栏，然后点击工具栏之后才能框选。能直接就进行框选么？
之前有开发者提过这个问题，不过已经自动closed了，详见：https://github.com/apache/echarts/issues/9214
想问下后续会支持该功能吗？

### What does the proposed API look like?

```js
backgroundColor: '#eee',
legend: {
data: ['bar', 'bar2', 'bar3', 'bar4'],
align: 'left',
left: 10
},
brush: {
toolbox: ['lineX', 'clear'],
xAxisIndex: 0
},
tooltip: {},
xAxis: {
data: xAxisData,
name: 'X Axis',
silent: false,
axisLine: {onZero: true},
splitLine: {show: false},
splitArea: {show: false}
},
yAxis: {

},
grid: {
left: 100
},
series: [
{
name: 'bar',
type: 'line',
stack: 'one',
itemStyle: itemStyle,
data: data1
}
]
```