Cart is not updated when Product is deleted or unpublished

Here's a slight modification of the patch, taking into account @Brolad's change in #29, and adding code to check if the product or product variation is not published. Please review :-)

This is the update for Commerce 2.37, based on @dubs patch from #30 🐛 Cart is not updated when Product is deleted or unpublished Needs work

Thanks for the patch!
Updated for Commerce 2.4

Seems like this should all be going into an AvailabilityChecker instead of jammed into the process method:

      $purchased_entity = $order_item->getPurchasedEntity();
      if (!$purchased_entity) {
        if ($order_item->hasPurchasedEntity()) {
          $order_items_to_remove[$order_item->id()] = $order_item;
        }
        continue;
      }
      // Check if the product or variation is unpublished.
      $product = $purchased_entity->getProduct();
      if (empty($product) || !$product->isPublished() || !$purchased_entity->isPublished()) {
        $order_items_to_remove[$order_item->id()] = $order_item;
        continue;
      }

Opened MR448 converting patch #32 into MR, and moved the availability logic into an AvailabilityChecker