请问sdk方式在表单中自定义组件，如何获取该组件的value，谢谢

```
自定义的组件会修改一些props中的值，作为组件的value,
如文档中例子，amis有默认传给组件的函数，用于组件把值提升上来，进而设置value么？

注意到custom中的onMount可以修改，sdk是否也可以用相同的方式取值？
谢谢~

{
type: 'page',
title: '表单页面',
body: {
type: 'form',
title: 'custom 组件',
body: [
{
type: 'custom',
name: 'myName',
label: '自定义组件',
onMount: (dom, value, onChange, props) => {
const button = document.createElement('button');
button.innerText = '点击修改';
button.onclick = event => {
onChange('new'); // 这个 onChange 方法只有放在表单项中才能调用
event.preventDefault();
};
dom.appendChild(button);
}
}
]
}
}

```

Start by comparing the custom component's onMount/onChange example with the SDK form integration described in the issue. Identify the relevant SDK entry point and existing value-propagation behavior; done requires a documented, reproducible way to update myName from the component, with the example verified.

Written by the indexing model from the issue text.