Add eslint-plugin-ie11

[mroderick]

This PR adds eslint-plugin-ie11, which would have prevented me from merging #1661, which caused a failing build (and more work for me). Instead, the author would have seen the error and fixed it.

Background

In IE11 Map and Set constructors do not accept arguments, but instead of throwing an error, they fail silently, and just produce the empty state.

// works in modern browsers, not in IE11
new Set([1, 2]);

How to verify - mandatory

1. Check out this branch
2. npm install
3. Add the code above to any linted JS file, save it
4. npm run lint
5. Observe the failure

[mantoni]

For this type of issues we cannot have enough automation. Thank for digging out the plugin. I didn't know about it 👍

[mroderick]

Thanks.

I also looked into eslint-plugin-compat (which I use elsewhere), but that doesn't catch this specific issue.

[mroderick]

I'll update the other projects to add this