[Feature Request] How to commit 'confirm' action when using custom content (vnode) of MessageBox

### Existing Component
是

### Component Name
MessageBox

### Description
I have something like this

```js
this.$msgbox({
title: 'Message',
message: h('my-input',{
props:{ value: foo }
on:{
input(val){
foo = val
},
commit(){
// QUESTION IS HERE
// when i press enter and the "my-input" component will emit a commit event
// and i want it do to an 'confirm' action in the messagebox.
// but how?
}
}
})
})
```