[Bug Report] An argument needs to be provided that tells whether the input event emitted by el-slider is triggered by setting value in JavaScript or by mouse etc.

### Element UI version
2.13.2

### OS/Browsers version
Google Chrome

### Vue version
3.0.0-beta.14

### Reproduction Link
https://codesandbox.io/s/heuristic-sound-qw5y9?file=/src/App.vue:11-266

### Steps to reproduce
```html

export default {
name: "App",
data() {
return {
value: 1
};
},
components: {
// HelloWorld
"el-slider": Slider
},
methods: {
handleSliderInput(v) {
console.log(arguments);
this.value = v;
},
buttonClick() {
console.log("button click");
this.value ;
}
}
};

```

### What is Expected?
There needs to be a value, passed in `handleSliderInput()`, that tells whether the `input` event is generated by change of the `value` property from JavaScript or manually by mouse.

### What is actually happening?
There is no such value that one could get in the input handler method like `handleSliderInput()`.