[Feature Request] There should be an option to not show any selected element, but only ` x` tag (x the number of selected elements)

### Existing Component
Yes

### Component Name
el-select

### Description
When `collapse-tags` prop is set to `true` and there isn't enough width to show selected elements, there should be an option not to show any selected element, but only ` x` tag (x the number of selected elements).

Reproduction link: https://codepen.io/batolye/pen/xxVQdeZ?editable=true%3Dhttps%3A%2F%2Felement.eleme.io%2F