🐛 [BUG] 分组箱线图的异常点没有分组

### 🐛 Bug description [Please make everyone to understand it]

> Please provide a link by forking these links [G2Plot](https://codesandbox.io/s/g2plot-issue-template-gzfdq?file=/index.ts) or GitHub repo, a minimal reproduction.

* _Required_ **Link to minimal reproduction**:

### 📷 Step to reproduce

```js
import { Box } from '@antv/g2plot';

const data = [
{ Species: 'I. setosa', type: 'SepalLength', value: 5.1, _bin: [4.3, 4.8, 5, 5.2, 5.8], outliers: [1, 10] },
{ Species: 'I. setosa', type: 'SepalWidth', value: 3.5, _bin: [2.3, 3.2, 3.4, 3.7, 4.4], outliers: [1, 10] },
{ Species: 'I. setosa', type: 'PetalLength', value: 1.4, _bin: [1, 1.4, 1.5, 1.6, 1.9], outliers: [1, 10] },
{ Species: 'I. setosa', type: 'PetalWidth', value: 0.2, _bin: [0.1, 0.2, 0.2, 0.3, 0.6], outliers: [1, 10] },
{ Species: 'I. versicolor', type: 'SepalLength', value: 7, _bin: [4.9, 5.6, 5.9, 6.3, 7], outliers: [1, 10] },
{ Species: 'I. versicolor', type: 'SepalWidth', value: 3.2, _bin: [2, 2.5, 2.8, 3, 3.4], outliers: [1, 10] },
{ Species: 'I. versicolor', type: 'PetalLength', value: 4.7, _bin: [3, 4, 4.35, 4.6, 5.1], outliers: [1, 10] },
{ Species: 'I. versicolor', type: 'PetalWidth', value: 1.4, _bin: [1, 1.2, 1.3, 1.5, 1.8], outliers: [1, 10] },
{ Species: 'I. virginica', type: 'SepalLength', value: 6.3, _bin: [4.9, 6.2, 6.5, 6.9, 7.9], outliers: [1, 10] },
{ Species: 'I. virginica', type: 'SepalWidth', value: 3.3, _bin: [2.2, 2.8, 3, 3.2, 3.8], outliers: [1, 10] },
{ Species: 'I. virginica', type: 'PetalLength', value: 6, _bin: [4.5, 5.1, 5.55, 5.9, 6.9], outliers: [1, 10] },
{ Species: 'I. virginica', type: 'PetalWidth', value: 2.5, _bin: [1.4, 1.8, 2, 2.3, 2.5], outliers: [1, 10] },
];

const groupBoxPlot = new Box('container', {
data,
xField: 'type',
yField: '_bin',
groupField: 'Species',
outliersField: 'outliers'
});

groupBoxPlot.render();

```

### 🏞 Expected result

异常点分组

### 🚑 Any additional [like screenshots]

* **G2Plot Version**:
* **Platform**:

Start with the Box plot entry point and run the supplied TypeScript reproduction using groupField and outliersField. Trace how grouped box plots render outliers, then verify that the outlier marks are separated by Species rather than combined; the grouped chart should match the expected result.

Written by the indexing model from the issue text.