feat(messaging): change usage of `Platform.isIos` to `defaultTargetPlatform` to allow mocking platform more easily

[fachrifaul]

Description

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Hard to mock Platform, need to change to defaultTargetPlatform

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[fachrifaul]

@fachrifaul - You need to remove this import from the same file you changed: https://github.com/firebase/flutterfire/actions/runs/7626531820/job/20773125499?pr=12183#step:5:241

Done

[google-oss-bot]

Hey @fachrifaul. We need more information to resolve this issue but there hasn't been an update in 7 weekdays. I'm marking the issue as stale and if there are no new updates in the next 7 days I will close it automatically.

If you have more information that will help us get to the bottom of this, just add a comment!

[google-oss-bot]

Since there haven't been any recent updates here, I am going to close this issue.

@fachrifaul if you're still experiencing this problem and want to continue the discussion just leave a comment here and we are happy to re-open this.