[Bug]: OneSignal.initialize is no longer idempotent on Android

What happened?

OneSignal.initialize(appId) used to be idempotent on iOS and Android. Since https://github.com/OneSignal/OneSignal-Cordova-SDK/commit/3c94a25887d90b468c80597fe3236f46658620dd, this is no longer the case on Android.

Currently, every time OneSignal.initialize(appId) is called, the current instance of OneSignalPush is added as a listener:

https://github.com/OneSignal/OneSignal-Cordova-SDK/blob/1e2f9e7763bc22c4c4f59d27d974676283b5c4d3/src/android/com/onesignal/cordova/OneSignalPush.java#L360-L364

The collection of listeners does not seem to be a Set and this is added to the listeners again and again. The end result is that the JS click event listener is called once for every invocation of OneSignal.initialize.

This causes problems in applications that are not 100% SPAs and navigate between different parts of the app using full-page reloads. In such a case, it is very difficult to determine if OneSignal.initialize has already been called or not and an idempotent version is much easier to use.

It can also cause problems when developing applications and using hotswapping/live reload.

Most likely related issues:

Steps to reproduce?

Create a test app that calls `OneSignal.initialize(appId)` several times
Click on a push notification
Registered click listeners will be called repeatedly

What did you expect to happen?

I expect to be able to call OneSignal.initialize(appId) as often as I want without any side effects on Android.

A simple solution would be to add a new isInitialized field to the OneSignalPush class and only add this as a listener if it has not been set.

OneSignal Cordova SDK version

5.2.4

Which platform(s) are affected?

[ ] iOS
[X] Android

Relevant log output

No response

Code of Conduct

[X] I agree to follow this project's Code of Conduct

OneSignal / OneSignal-Cordova-SDK