WIP feat(fcm): Add Support for AndroidConfigV2

[jonathanedey]

This change implements support for the Android v2 API and It deprecates v1 AndroidConfig structures and replaces them with the new AndroidConfigV2 structures.

• Adds AndroidConfigV2, AndroidNotificationV2, AndroidRemoteNotification, and AndroidBackgroundSyncMessage types.
• Deprecates AndroidConfig, AndroidNotification, and AndroidNotificationProxy

[gemini-code-assist]

Code Review

This pull request introduces the V2 Android messaging configuration (AndroidConfigV2 and AndroidNotificationV2) to the messaging package, deprecating the older V1 Android configuration types. It includes JSON marshalling/unmarshalling implementations, validation logic, unit tests, and usage snippets. Feedback on the changes suggests resetting the VibrateTimingMillis slice in AndroidNotificationV2.UnmarshalJSON before appending to prevent duplicate values when the receiver struct is reused.