Fix EuiIcon so webpack can build dynamic require contexts

[pugnascotia]

Summary

The work to remove TSLint in favour of ESLint has the side effect of "fixing" a lint failure in EuiIcon. It changed a plain string concatenation into a string template. Normally this would be fine, but this particular string concatenation is used to load icons dynamically, and Webpack can't build a dynamic require context from the compiled version of the template string.

Revert the change and add a lint directive to stop it recurring.

I built and linked the package, and tried it out in Cloud UI to ensure it was working as expected.

Checklist

• This was checked in mobile
• This was checked in IE11
• This was checked in dark mode
• Any props added have proper autodocs
• Documentation examples were added
• A changelog entry exists and is marked appropriately
• This was checked for breaking changes and labeled appropriately
• Jest tests were updated or added to match the most common scenarios
• This was checked against keyboard-only and screenreader scenarios
• This required updates to Framer X components

[thompsongl]

LGTM

I'm likely going to release 11.3.1 today and this will be in it

[pugnascotia]

Nice one Greg, please let @claracruz know when you've released it.