fix: 'Flutter.initializeApp' error on Android

[ihorvitruk]

Description

Error:

E/flutter ( 6109): [ERROR:flutter/runtime/dart_vm_initializer.cc(39)] Unhandled Exception: [core/not-initialized] Firebase has not been correctly initialized.
E/flutter ( 6109): 
E/flutter ( 6109): Usually this means you've attempted to use a Firebase service before calling `Firebase.initializeApp`.
E/flutter ( 6109): 
E/flutter ( 6109): View the documentation for more information: https://firebase.flutter.dev/docs/overview#initialization
E/flutter ( 6109):     
E/flutter ( 6109): #0      MethodChannelFirebase.initializeApp (package:*******.flutter_plugins.firebase_core.interface/src/method_channel/method_channel_firebase.dart:99:9)
E/flutter ( 6109): <asynchronous suspension>
E/flutter ( 6109): #1      Firebase.initializeApp (package:firebase_core/src/firebase.dart:40:31)
E/flutter ( 6109): <asynchronous suspension>

Bug explanation:
Default FirebaseApp is not created, if FirebaseOptions instanceis not passed directly toFirebase.initializeApp` function.

Fix explanation:

• modify MethodChannelFirebase to create default app also if options are null
• modify [FlutterFirebaseCorePlugin.java to check whether options are null. If yes - retrieve firebase options from resource:

options = FirebaseOptions.fromResource(applicationContext);

Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See [Contributor Guide]).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (melos run analyze) does not report any problems on my PR.
• I read and followed the [Flutter Style Guide].
• I signed the [CLA].
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change.
• No, this is not a breaking change.

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[Salakar]

I couldn't push changes to this PR so I've pushed to a new branch and made a replacement PR: #8566