Proposal: warn on /index imports

[mike1808]

My IDE likes to add /index to the import path when I specify some folder path with index.js file in it. For example:

- module
    - index.js

- file.js

// file.js
import module from './module'

and it becomes

// file.js
import module from './module/index'

Can we have a rule which disallows explicit specification of the index file?

[ljharb]

This seems like it'd be handled by #912 - since that could be shortened to ./module, it would warn.