[core] Update Flutter to Version 3.16.0 (#70)

Update the used Flutter version to 3.16.0 and all Flutter packages to
their latest version.

This commit also fixes all of the newly added analysis options and the
layout changes introduced with the new Flutter version (e.g. we have to
set the "tabAlignment" property in the "TabBar" widget).

app/lib/widgets/settings/settings_info.dart

@@ -13,7 +13,7 @@ import 'package:feeddeck/utils/openurl.dart';
 /// Here the user can find information the version of the app and the links to
 /// the website, the GitHub repository and the X account.
 class SettingsInfo extends StatefulWidget {
-  const SettingsInfo({Key? key}) : super(key: key);
+  const SettingsInfo({super.key});
 
   @override
   State<SettingsInfo> createState() => _SettingsInfoState();