Rule proposal: no-duplicate-named

I just noticed the the following is considered to be valid syntax by both espree and babel-eslint.

import {a, a, b as a, c as a} from 'foo';

We should add a rule that forbids:

• Importing a named export twice: {a, a}
• Importing a named export and naming it after another imported named export: {a, b as a}
• Importing a named export and naming it after the name of another renamed imported named export: {b as a, c as a}

To discuss:

• Importing a named export and naming it the original name of an other renamed imported named export: {b as a, c as b}

I'm pretty sure we had a rule to forbid import {b as a} from 'foo' when a is also a named export of that module, but I don't remember which one. If we don't, let me know, and I'll create an issue, because that sounds like a nice style issue to have. That might fill the role of the last to discuss item?

I propose the name no-duplicate-named, but I'm open to better names :)

The issue names no files, tests, or entry points. First resolve the proposed rule's name and the disputed {b as a, c as b} behavior, then identify the existing import-rule implementation and tests; done means duplicate named imports are consistently rejected according to the agreed cases.