fix(messaging, ios): prevent getInitialMessage from being null at the start of the app

[Lyokone]

Description

Tested the different behavior:

• Receiving multiples notification and check the good one is in the initialMessage
• Receiving multiple notifications but opening the app with the icon
• Opening the app in background state from a notification and check that the initialMessage is null
• Opening the app in terminated state from a notification and check that the initialMessage is correct

Related Issues

#9906

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[mikehardy]

The debate between whether to "consume" the initial message or not was (is?) contentious in react-native-firebase. Because there is possibility of hot-reload etc, we decided to consume them. Otherwise on hot reload the app reacts to the initial native message again which is unwanted. Same with notification and dynamic link

[Lyokone]

The debate between whether to "consume" the initial message or not was (is?) contentious in react-native-firebase. Because there is possibility of hot-reload etc, we decided to consume them. Otherwise on hot reload the app reacts to the initial native message again which is unwanted. Same with notification and dynamic link

Super interesting, didn't thought about this, I'll revert back to the previous behavior :)