Address Ship Review issues with entitlement expiration (#2628)

Task/Issue URL: https://app.asana.com/0/1203137811378537/1206896148261286/f
Tech Design URL:
CC:

Description:

This PR addresses some Ship Review issues with entitlement expiration not being picked up by adding entitlementsDidChange and accountDidSignOut notification handling

Steps to test this PR:

Subscribe to PP
Remove sub from device
VPN should stop and be removed from Settings.app
Revoke the entitlements
Open another app and go back to the app
The app should detect the entitlement change and show messaging & stop the VPN

DuckDuckGo/MainViewController.swift

@@ -1355,6 +1355,18 @@ class MainViewController: UIViewController {
                 self?.onNetworkProtectionAccountSignIn(notification)
             }
             .store(in: &vpnCancellables)
+        NotificationCenter.default.publisher(for: .entitlementsDidChange)
+            .receive(on: DispatchQueue.main)
+            .sink { [weak self] notification in
+                self?.onEntitlementsChange(notification)
+            }
+            .store(in: &vpnCancellables)
+        NotificationCenter.default.publisher(for: .accountDidSignOut)
+            .receive(on: DispatchQueue.main)
+            .sink { [weak self] notification in
+                self?.onNetworkProtectionAccountSignOut(notification)
+            }
+            .store(in: &vpnCancellables)
 
         NotificationCenter.default.publisher(for: .vpnEntitlementMessagingDidChange)
             .receive(on: DispatchQueue.main)
@@ -1409,6 +1421,27 @@ class MainViewController: UIViewController {
         tunnelDefaults.resetEntitlementMessaging()
         os_log("[NetP Subscription] Reset expired entitlement messaging", log: .networkProtection, type: .info)
     }
+
+    @objc
+    private func onEntitlementsChange(_ notification: Notification) {
+        Task {
+            guard case .success(false) = await AccountManager().hasEntitlement(for: .networkProtection) else { return }
+
+            tunnelDefaults.enableEntitlementMessaging()
+
+            let controller = NetworkProtectionTunnelController()
+            await controller.stop()
+        }
+    }
+
+    @objc
+    private func onNetworkProtectionAccountSignOut(_ notification: Notification) {
+        Task {
+            let controller = NetworkProtectionTunnelController()
+            await controller.stop()
+            await controller.removeVPN()
+        }
+    }
 #endif
 
     @objc