[PM-24280] Remove account service from state (#15828)

* Introduce ActiveUserAccessor

* Use ActiveUserAccessor over AccountService

* Updates tests and testing utils to support ActiveUserAccessor

* Update all injection points

* Fix types test

* Use ternary instead

libs/common/src/auth/services/default-active-user.accessor.ts

@@ -0,0 +1,19 @@
+import { map, Observable } from "rxjs";
+
+import { UserId } from "@bitwarden/user-core";
+
+import { ActiveUserAccessor } from "../../platform/state";
+import { AccountService } from "../abstractions/account.service";
+
+/**
+ * Implementation for Platform so they can avoid a direct dependency on AccountService. Not for general consumption.
+ */
+export class DefaultActiveUserAccessor implements ActiveUserAccessor {
+  constructor(private readonly accountService: AccountService) {
+    this.activeUserId$ = this.accountService.activeAccount$.pipe(
+      map((a) => (a != null ? a.id : null)),
+    );
+  }
+
+  activeUserId$: Observable<UserId | null>;
+}