android: hidden notification when in background

[m1ga]

Current behavior:

when you send a data notification without a title it will handle it as a "hidden" notification and only set an intent for the next app start (as there is no notification). BUT if the app is still running in the background it should still trigger didReceiveMessage. Currently it doesn't as we set showNotification = false.

This PR:

Will return true so it still tries to call didReceiveMessage but still sets the ti.firebase.messaging.hidden-notification in case it was closed.

Testing it with a Slack user at the moment

firebase.cloudmessaging-android-3.5.4.zip

Test:

• create a push project
• start the app and put it into the background
• send a data notification without a title attribute
• check if didReceiveMessage is called