[Fix] iOS notifications clicked event to fire on cold start

[shepherd-l]

Description

One Line Summary

Fixes iOS notifications clicked event to fire when the app was cold started from clicking a notification.

Details

Motivation

Fixes #638 iOS bug where Notifications.Clicked event is set but does not fire when clicking the notification cold starts the app.

Testing

Manual testing

Tested clicking on notifications when the app in the foreground, background, and closed, app build with Unity 2021.3.16f1 of the OneSignal example app on a physical iPhone 12 with iOS 15.5.

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
• I have reviewed this PR myself, ensuring it meets each checklist item

---

This change is