Use analyzer.language instead of analyzer.strong-mode

[maRci002]

v3.0.0 version supports Dart ^2.17.0

These lines:

  strong-mode:
    implicit-casts: false
    implicit-dynamic: false

Should be changed to:

  language:
    strict-casts: true
    strict-inference: true
    strict-raw-types: true

Source:
https://dart.dev/guides/language/analysis-options#enabling-additional-type-checks

[maRci002]

Note: strict-inference: true might be pain for someone.

Consider these two examples:
Future.delayed(const Duration(seconds: 1));
Navigator.of(context).push(MaterialPageRoute(builder: (BuildContext context) => const Scaffold()));

In case of strict-inference: true this should look like this:
Future<void>.delayed(const Duration(seconds: 1));
Navigator.of(context).push<void>(MaterialPageRoute(builder: (BuildContext context) => const Scaffold()));