[Feature Request] The support of ESM

### Existing Component
No

### Component Name
Whole Project

### Description
Now, the vue2 has supported esm to build more efficient project. So, I want to rebuild my project via esm. But I found that element-ui not provide the supportation.
Is there any plan to support it?

Best regards.

The followings are the error message.
```
ERROR Failed to compile with 2 errors 下午4:59:09

error in ./node_modules/element-ui/packages/scrollbar/src/main.js

Module parse failed: Unexpected token (65:6)
You may need an appropriate loader to handle this file type, currently no
loaders are configured to process this file. See https://webpack.js.org/
concepts#loaders
| }, this.$slots.default);
| const wrap = (
>