fieldSet不支持columnCount

#### 实现场景：
fieldSet不支持columnCount

#### 存在的问题：
fieldSet不支持columnCount

#### 当前方案：
```
{
"type": "form",
"title": "表单",
"body": [
{
"type": "fieldSet",
"title": "基本信息",
"body": [
{
"label": "文本框",
"type": "input-text",
"name": "text"
},
{
"type": "input-text",
"label": "s",
"name": "s"
}
],
"columnCount": 2
}
],
"id": "u:ca1804a19fca",
"mode": "horizontal"
}
```

The issue names no source file or test. Start by locating the TypeScript implementation of fieldSet and reading how its body layout is rendered; completion should make the supplied configuration's two input fields appear in two columns.

Written by the indexing model from the issue text.