Code quality fixes

Problem/Motivation

While phpstan tests pass on the current main branch there are several issues with code quality revealed by a higher strictness level.

Steps to reproduce

Proposed resolution

Remaining tasks

src/EventSubscriber/ProductReviewEventSubscriber.php:
$product is never empty. Check that $product is an instance of ProductInterface instead. Don't use return in a function that doesn't return anything.

src/Plugin/Field/FieldType/OverallRatingItem.php:
getEntity() will return an entity or NULL. If $parent is NULL then instanceof ProductInterface will evaluate to false. Checking if $parent is set is not needed.

src/OverallProductRating.php:
Fix phpstan error Access to an undefined property Drupal\Core\Field\FieldItemListInterface::$score

User interface changes

API changes

Data model changes