将 amis 当成 UI 库用时，Select组件不支持 selectMode 属性

#### 实现场景：
将 amis 当成 UI 库用时，Select 组件不支持 selectMode 属性，无法实现下拉选项为 tree 结构

#### 存在的问题：
Select 组件不支持 selectMode 属性，无法实现下拉选项为 tree 结构

#### 当前方案：
请粘贴你当前方案的完整 amis schema 代码...

```

import { ReactInVue } from 'vuera'
import { Select } from 'amis';

export default {
name: 'SelectDemo',
data() {
return {
treeOptions: [
{
"label": "Folder A",
"value": 1,
"children": [
{
"label": "file A",
"value": 2
},
{
"label": "file B",
"value": 3
}
]
},
{
"label": "file C",
"value": 4
},
{
"label": "file D",
"value": 5
},
]
}
},
components: {
Select: ReactInVue(Select),
}
}

```

Start with the amis Select component and the provided SelectDemo schema, then trace how options and the selectMode prop are handled. Verify the treeOptions example with selectMode set to "tree" and multiple selection, and confirm the component renders and selects the nested tree values as intended.

Written by the indexing model from the issue text.