【V5】ColorScale设置range为多个值时，只有前两个颜色生效

### 问题描述

> 【版本】：`@antv/g2@^5.1.12`
>
> 【场景描述】：散点图增加自定义的多色图例
>
> 【问题】：设置两个以上颜色时，仅前两个颜色生效
>
> 【代码示例如下】：
>
```javascript
// 示例来源于 https://g2.antv.antgroup.com/zh/examples/general/point/#point-basic
import { Chart } from '@antv/g2';

const chart = new Chart({
container: 'container',
autoFit: true,
});

chart
.point()
.data({
type: 'fetch',
value:
'https://gw.alipayobjects.com/os/basement_prod/6b4aa721-b039-49b9-99d8-540b3f87d339.json',
})
.encode('x', 'height')
.encode('y', 'weight')
.encode('color', 'height')
.scale({
'color': {
type: 'linear',
// 连续型color的度量range仅前两个有效
range: ['red', '#aaa', 'blue']
}
});

chart.render();
```
### 效果图如下

以上。
谢谢

### 平台
- 操作系统: [Windows]
- 网页浏览器: [Google Chrome, Edge]

Reproduce the issue with the provided G2 point example and its linear color scale using range ['red', '#aaa', 'blue']. Trace the continuous color-scale handling to determine why only two range entries are used. Done means all supplied colors participate in the rendered scatter plot, with regression coverage for the multi-color range.

Written by the indexing model from the issue text.