In the [bug report] pagination function, the drop-down box of the number selector displayed on each page does not support setting Popper options and Popper append to body

### Element UI version
2.8.2

### OS/Browsers version
版本 83.0.4103.116（正式版本） （64 位）

### Vue version
2.5.17

### Reproduction Link
https://codepen.io/pen/?&editable=true&prefill_data_id=ab116d80-a4a6-0138-0373-02420aff001a&referer=https%3A%2F%2Felement.eleme.cn%2F2.8%2F

### Steps to reproduce
迁移列表页-点击添加主机按钮-出现的dialog 中表格的分页下拉选择框定位不准

### What is Expected?
组件支持设置popper-append-to-body 及 popper-options 属性

### What is actually happening?
只把el-select 的popper-class 暴露了出来，但是当下拉选择框定位不准时并不支持设置popper-append-to-body 属性