fix(react-native-branch): Re-init branch session when resumed from background

[morgan-cromell]

Why

The react-native-branch plugin used the OnCreate lifecycle hook to call RNBranchModule.InitSession. This caused the session to only be initialized on first start of the application and not when switching from foreground to background.

How

According to the official docs you should use the OnStart hook to intialize Branch, but as this does not exists on ReactActivityLifecycleListener onResume was the closest one.

Test Plan

Tried to send an event to branch from react-native with

const event = new BranchEvent('TEST');
event.logEvent();

I used Android studio to monitor network traffic and see that the event is sent to Branch.

Before this fix this stopped working if the app was sent to the background and later resumed.

[jvgeee]

Can this be merged in please?