fix: expo users reported app crash on didFailToRegisterForRemoteNotificationsWithError

[ami-aman]

part of: https://linear.app/customerio/issue/MBL-141/expo-50-with-version-100-beta15-crash-startup-app-on-ios

Steps to reproduce the bug
There are no direct steps reported by the customer to reproduce the issue.
Other known ways to reproduce didFailToRegisterForRemoteNotificationsWithError :

• Settings -> Notifications -> your app
• Turn off notifications
• Go back to app and attempt to register for push notifications
  OR
• Turn off internet
• Attempt to register for push notifications

How this PR fixes the bug
Let's understand what the bug is first. The issue is with the instance of messagingPush that is not initialised by the time it is called and hence the app crashes. This PR fixes it by using Self.shared instead of messagingPush and calls deleteDeviceToken method that further calls messagingPush.deleteDeviceToken() that has a living instance of messagingPush and hence the code is executed without any issue.

What you have done to test this PR
Since there are no steps reported by the customer, I reproduced the issue by calling messagingPush.deleteDeviceToken() in didRegisterForRemoteNotificationsWithDeviceToken instead of into method didFailToRegisterForRemoteNotificationsWithError. This helped me figure out where the issue lies.

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[github-actions]

Sample app builds 📱

Below you will find the list of the latest versions of the sample apps. It's recommended to always download the latest builds of the sample apps to accurately test the pull request.

---

• CocoaPods-FCM: aman/crash-fix (1709632239)
• APN-UIKit: aman/crash-fix (1709632200)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 56.79%. Comparing base (251a958) to head (b6b9ec5).
Report is 3 commits behind head on main.

❗ Current head b6b9ec5 differs from pull request most recent head 1f16b0e. Consider uploading reports for the commit 1f16b0e to get more accurate results

Files	Patch %	Lines
...essagingPushAPN/MessagingPushAPN+PushConfigs.swift	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #575      +/-   ##
==========================================
+ Coverage   56.25%   56.79%   +0.53%     
==========================================
  Files         132      132              
  Lines        3715     3717       +2     
==========================================
+ Hits         2090     2111      +21     
+ Misses       1625     1606      -19     

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[levibostian]

Can you write tests for this change?

It would be great if we had a test that could reproduce the crash and then show that after this change the test passes.

[ami-aman]

Can you write tests for this change?

It would be great if we had a test that could reproduce the crash and then show that after this change the test passes.

@levibostian I started writing test cases for this swizzled method but it looks like a larger effort and updates than I anticipated. As this fix is a result of a crash report by a customer, would would mind if I open a tech debt and let go this fix ?

[levibostian]

LGTM

I checked the CI status checks that are failing in this PR and they are also failing in main. Therefore, it's OK with me to merge this PR with the current failed status checks and fix the main branch in a separate PR.