[Fix]Multiple OneSignal instance

[shepherd-l]

Description

One Line Summary

Fixes additional instance of OneSignalAndroid or OneSignaliOS from being created when calling OneSignal methods in Awake().

Details

Motivation

Removes logged error "Additional instance of OneSignalAndroid/OneSignaliOS created."
Reproducible when calling OneSignal.Debug.LogLevel = LogLevel.Verbose; in Awake().

Scope

OneSignal.Default now manages the platform instance entirely instead of setting it again in platform initialization. Since OneSignal.Default already creates the platform instance in _getDefaultInstance(), we can remove the setter and the internal classes that used it: OneSignalAndroidInit, OneSignaliOSInit, OneSignalNativeInit.

Testing

Manual testing

Tested calling OneSignal debug and initialization methods in Awake(), app build with Unity 2022.3.10f1 of the OneSignal example app on a emulated Pixel 4 with Android 12 and a physical iPhone 12 with iOS 17.5.1.

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
  • If it is hard to explain how any codes changes are related to each other then it most likely needs to be more than one PR
• 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.
  • Simplify with less code, followed by splitting up code into well named functions and variables, followed by adding comments to the code.
• I have reviewed this PR myself, ensuring it meets each checklist item
  • WIP (Work In Progress) is ok, but explain what is still in progress and what you would like feedback on. Start the PR title with "WIP" to indicate this.

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