[firebase_messaging] fix onLaunch being called again when resuming an application from Recents screen

[MaikuB]

Description

On Android, there is an issue where it is possible for the onLaunch callback to be invoked multiple times. One way to produce this is

• Sent a notification a device when the app is terminated
• Tap on the notification to launch the app -> onLaunch should be called
• Tap back until the application is in the background
• Open the Recents screen (aka recent task/app list) and go back to the app
• onLaunch is called again

This is happening as when the application starts up again, it will call configure method that will in turn process the intent. However, when processing the intent it should check to make sure that the app isn't launched via the Recents screen. This PR as this guard in to prevent the issue from happening.

Note: for some reason, pub is failing to resolve the dependencies (didn't happen in the past) so I cannot try to out properly but had to a similar fix for my own plugin for local notifications. This is why I haven't ticked the box that the analyzer doesn't report any problems

Related Issues

• [firebase_messaging] clear intent after onLaunch invoked on Android #1887

Checklist

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Breaking Change

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