Workaround for lack of $form_state in ProductVariationAjaxChangeEvent

Problem/Motivation

https://www.drupal.org/project/commerce/issues/3019102

Steps to reproduce

Install the module and fill a quantity field in the cart form of a product with attributes. Then change an attribute so that a new variation is selected. The price does not reflect the change.

Proposed resolution

As mentioned in the above issue, override the ProductVariationAttributesWidget field widget.