[Feature Request] There is no prop for the Input of MessageBox, such as maxLength and show-word-limit

### Existing Component
是

### Component Name
MessageBox

### Description
- There is no prop for the Input of MessageBox, such as maxLength and show-word-limit

### Expected results

```javascript
let promptRes = await this.$prompt('message', {
title: 'Title',
type: 'info',
inputProps: {
maxlength: 10,
'show-word-limit': true
},
inputPlaceholder: 'please input',
inputValidator: value => {
// ...
return true
}
}).then(({ value }) => value).catch(() => '')
```