[PLAT-7208] Fix missing sessions when started in background state

[nickdowell]

Goal

Fix a regression (introduced in release v6.9.5 by #1108) where the session was not captured at launch if Bugsnag was started before willFinishLaunchingWithOptions in iOS apps that do not adopt the UIScene life-cycle.

Overview

If Bugsnag is started early in the app life-cycle, before the app delegate's willFinishLaunchingWithOptions method is called, then applicationState is reported as .background and Bugsnag does not start a session.

In iOS apps that do not adopt the UIScene life-cycle, no willEnterForegroundNotification is posted during launch and consequently no session was being started until the app was resumed from the background state. A didBecomeActiveNotification is posted during launch.

Changeset

The session tracker now starts a session in response to didBecomeActiveNotification as well as willEnterForegroundNotification.

Notification registration logic has been moved to BugsnagSessionTracker to make it more testable.

Testing

Reproduced the issue and verified the fix using a test app.

Added unit test cases to verify that

• A session is started upon receiving UIApplicationDidBecomeActiveNotification alone
• Multiple calls to handleAppForegroundEvent do not result in multiple sessions

E2E tests cannot test this because the fixture app cannot start Bugsnag early enough in the app's life-cycle.

[github-actions]

Infer: No issues found 🎉

OCLint: No issues found 🎉

Bugsnag.framework binary size decreased by 280 bytes from 1,156,400 to 1,156,120 🎉

Generated by 🚫 Danger