[Bug Report] Dialog : drag and drop mouse --> auto close dialog

### Element UI version
2.15.7

### OS/Browsers version
Mac Os

### Vue version
2.6.14

### Reproduction Link
https://codepen.io/chinh-le-tuan/pen/GROdbXV

### Steps to reproduce
open a dialog
drag to select text and drop mouse

Observe that it close dialog automatically (don't click out)

### What is Expected?
open a dialog
drag to select text and drop mouse --> don't close dialog

### What is actually happening?
I think conflict mouse up and click event, please fix it