Make LinkNewDeviceScreen fall back to the App Lock PIN code when there's no passcode. (#5794)

* Fall back to the AppLock PIN code when there's no passcode.

* Add extra tests on the LinkNewDeviceFlowCoordinator.

* Misc tweaks for clarification.

* Regenerate snapshots.

ElementX/Sources/Other/AccessibilityIdentifiers.swift

@@ -57,6 +57,7 @@ enum A11yIdentifiers {
     }
     
     struct AppLockScreen {
+        let cancel = "app_lock-cancel"
         func numpad(_ digit: Int) -> String {
             "app_lock-numpad_\(digit)"
         }