feat(android,core): allow initializing default Firebase apps via FirebaseOptions.fromResource on Android

[Salakar]

Description

Supersedes #8535 . Additionally updated example app to support initializing a default app from Android resources.

Files that should be reviewed can be seen here: https://github.com/firebase/flutterfire/pull/8566/files?file-filters%5B%5D=.dart&file-filters%5B%5D=.java&show-deleted-files=false&show-viewed-files=false (there are other changes since I had to update the Android project for latest Flutter SDK changes)

Logs from local testing showing this is working:

I/flutter (15634): Currently initialized apps: []
I/flutter (15634): Initialized default app FirebaseApp([DEFAULT]) from Android resource
I/flutter (15634): Currently initialized apps: [FirebaseApp([DEFAULT])]
I/flutter (15634): Current options for app [DEFAULT]: {apiKey: xxxxxxxxx, appId: 1:406099696497:android:0d4ed619c031c0ac3574d0, messagingSenderId: 406099696497, projectId: flutterfire-e2e-tests, authDomain: null, databaseURL: https://flutterfire-e2e-tests-default-rtdb.europe-west1.firebasedatabase.app, storageBucket: flutterfire-e2e-tests.appspot.com, measurementId: null, trackingId: null, deepLinkURLScheme: null, androidClientId: null, iosClientId: null, iosBundleId: null, appGroupId: null}

Related Issues

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Breaking Change

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[russellwheatley]

LGTM