(Billing) [PM-27562] Create PremiumInterestStateService (#17139)

Creates a `PremiumInterestStateService` that manages state which conveys whether or not a user intends to setup a premium subscription. Implemented in Web only. No-op for other clients.

This will apply for users who began the registration process on https://bitwarden.com/go/start-premium/, which is a marketing page designed to streamline users who intend to setup a premium subscription after registration.

libs/angular/src/billing/services/premium-interest/noop-premium-interest-state.service.ts

@@ -0,0 +1,14 @@
+import { Injectable } from "@angular/core";
+
+import { UserId } from "@bitwarden/user-core";
+
+import { PremiumInterestStateService } from "./premium-interest-state.service.abstraction";
+
+@Injectable()
+export class NoopPremiumInterestStateService implements PremiumInterestStateService {
+  async getPremiumInterest(userId: UserId): Promise<boolean | null> {
+    return null;
+  } // no-op
+  async setPremiumInterest(userId: UserId, premiumInterest: boolean): Promise<void> {} // no-op
+  async clearPremiumInterest(userId: UserId): Promise<void> {} // no-op
+}

libs/angular/src/billing/services/premium-interest/premium-interest-state.service.abstraction.ts

@@ -0,0 +1,14 @@
+import { UserId } from "@bitwarden/user-core";
+
+/**
+ * A service that manages state which conveys whether or not a user has expressed interest
+ * in setting up a premium subscription. This applies for users who began the registration
+ * process on https://bitwarden.com/go/start-premium/, which is a marketing page designed
+ * to streamline users who intend to setup a premium subscription after registration.
+ * - Implemented in Web only. No-op for other clients.
+ */
+export abstract class PremiumInterestStateService {
+  abstract getPremiumInterest(userId: UserId): Promise<boolean | null>;
+  abstract setPremiumInterest(userId: UserId, premiumInterest: boolean): Promise<void>;
+  abstract clearPremiumInterest(userId: UserId): Promise<void>;
+}