Like to confirm if we can set `android:exported="false"` for instance id service and messaging service.

I tested by keeping `android:exported="false"` and notifications are working fine.

```
<service
    android:name=".MyFirebaseMessagingService"
    android:exported="false">
    <intent-filter>
        <action android:name="com.google.firebase.MESSAGING_EVENT"/>
    </intent-filter>
</service>

<service
    android:name=".MyFirebaseInstanceIDService"
    android:exported="false">
    <intent-filter>
        <action android:name="com.google.firebase.INSTANCE_ID_EVENT"/>
    </intent-filter>
</service>

```