MobileAds.init from a Background thread

[LTPhantom]

Description

Calling MobileAds init from background thread.

Related Issues

#1135

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[malandr2]

Appears the AppLovin APIs have changed - they are causing a failure: https://github.com/googleads/googleads-mobile-flutter/blob/main/samples/admob/mediation_example/ios/Runner/AppDelegate.m#L46

[LTPhantom]

Appears the AppLovin APIs have changed - they are causing a failure: https://github.com/googleads/googleads-mobile-flutter/blob/main/samples/admob/mediation_example/ios/Runner/AppDelegate.m#L46

There is a major change on latest AppLovin which is affecting the sample. For now I limited the version used by it, but we might need to rethink the sample in the future.