Feat: add public log listener methods

[jkasten2]

Description

One Line Summary

Adds the following new public methods to allow an app developer to capture logs as strings at runtime.

Details

Adds the following new public methods:

• OneSignal.Debug.addLogListener
• OneSignal.Debug.removeLogListener

These new methods provide a way to capture all SDK log entires at runtime, allowing the app developer to store these and/or send them to their server.

The log listener is independent of logLevel, all message are always sent to listeners.

Motivation

App developers want a way to capture all SDK logs and send them to their server to debug issues in production.

Scope

Only add new methods to OneSignal.Debug to allow of capturing logs at runtime.

Testing

Unit testing

Added a new LoggingTests class to cover the new public methods.

Manual testing

Tested on an Android 15 emulator.

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
  • Failing due to unrelated flaky OperationRepoTests test.
• 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

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This change is 

[jinliu9508]

I added Logging.log inside the onLogEvent and it looks like it is creating logs non-stop. Should we add a note to not calling log inside the log event?

[jkasten2]

I added Logging.log inside the onLogEvent and it looks like it is creating logs non-stop. Should we add a note to not calling log inside the log event?

• The OneSignal Logging class shouldn't be used outside of the OneSignal SDK, it's been public since the 5.0.0 release but it was not indented and isn't documented.
• The logging listener isn't intended to be used inside the SDK, only externally by apps.

Given the above I don't think we need account for this.