The symfony inflector library is not pluralizing certain words correctly

Problem/Motivation

Symfony string inflector is buggy...

Several examples:

use Symfony\Component\String\Inflector\EnglishInflector;
$inflector = new EnglishInflector();
$inflector->pluralize('coupon'); // This returns "coupa".
$inflector->pluralize('coupons'); // This will return "couponss".

I tried the same with the Doctrine inflector, which we stopped using as part of #3117772: Doctrine\Common\Inflector\Inflector no longer in D9 and I got the expected results (i.e "coupons") for both strings).

My proposal is to switch back to using the Doctrine inflector, and require that directly.

The main issue this is causing is the promotion--coupons relationship that's being renamed to "promotion-coupa"...