Add Array.includes polyfill to support IE11 and Opera Mini

Problem/Motivation

A polyfill for Array.includes() is needed for Internet Explorer 11 and Opera Mini.

This is one of the three polyfills from 📌 Provide a new library to replace jQuery UI autocomplete Needs work and we are now addressing each in their own issue.

Note: While it is currently a nice-to-have, it will be necessary for the new Autocomplete issue 📌 Provide a new library to replace jQuery UI autocomplete Needs work to land as it includes a library that uses a non-polyfilled Array.includes. It's also a nice way to phase out the indexOf hack, which won't be necessary in Drupal 10 since IE11 won't be supported.