* Include valid couponCode and promotionCode in `payment-page-view` and `payment-page-form-submit` analytics events
* Update payment event types
* Remove obsolete comment
* fix: only send validated coupon and promotion codes in analytics event
* Add coupon name for the analytics events
* Update test to include the coupon name for analytics
* Remove coupon code from analytics
* Simplify promotion code validation using coupon.code
* Remove undefined
* Allow access to promotion code
* Remove `lastValidatedPromotionCode` and compare against coupon code from the preview response
* Fix test setup to initialize coupon code
* Keep the submit button enabled only when the coupon code is either empty or successfully validated by the backend
* Update test coupon code value to TEST_COUPON
GitOrigin-RevId: b12fa147d91fd3b90b59bc77868a0786ddb633b7