[web] Remove SubscriptionFormatters, format subscription dates in the frontend (#36409)

* [web] Remove SubscriptionFormatters, format subscription dates in the frontend

Replace the server-formatted nextPaymentDueAt/nextPaymentDueDate/
trialEndsAtFormatted fields with the raw periodEnd date and format in
the React dashboard (same strings as before, English + UTC). Also
consolidate hand-rolled trial checks onto isInFreeTrial /
SubscriptionHelper.isInTrial.

* [web] Remove the now-unused dateformat dependency

* [web] Address review: payment-dates unit test, UTC dates in acceptance test

Add a dedicated unit test asserting the exact formatted strings from
formatPaymentDate/formatPaymentDateTime, and use explicit UTC timestamps
in the SubscriptionDashboard acceptance fixtures instead of
local-timezone Date constructors.

GitOrigin-RevId: 16ac4f1098b14ef9f1478d22cf39c1357ead7dea

services/web/types/subscription/dashboard/subscription.ts

@@ -37,12 +37,10 @@ type PaymentProviderRecord = {
   additionalLicenses: number
   addOns: PaymentProviderAddOn[]
   totalLicenses: number
-  nextPaymentDueAt: string
-  nextPaymentDueDate: string
+  periodEnd: string
   currency: CurrencyCode
   planPrice: number
   state?: SubscriptionState
-  trialEndsAtFormatted: Nullable<string>
   trialEndsAt: Nullable<string>
   activeCoupons: PaymentProviderCoupon[]
   accountEmail: string