Update leancode_lint to use new language modes and remove strong-mode

[bartekpacia]

When using leancode_lint on Flutter beta, it spits out:

another example:

The cause lies here:

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

We should change it to:

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

as suggested by Customizing static analysis docs.

Learn more:

• https://dart.dev/guides/language/analysis-options#enabling-additional-type-checks
• Remove old fields from analysis_options.yaml dart-lang/sdk#50680
• Remove analyzer's deprecated analysis modes: no-implicit-casts and no-implicit-dynamic dart-lang/sdk#50679

cc: @Albert221 @shilangyu

[shilangyu]

Sounds good to me, I think we can proceed with the change, but without the strict-raw-types field since we did not use it before

[Albert221]

I'm okay with the changes, as well as adding the strict-raw-types. We should remember to bump minimum Dart version and the package MAJOR though

[shilangyu]

We should remember to bump minimum Dart version

To which version? Afaik the current constraint is correct (?), >=2.17.0

[bartekpacia]

I think the best way to test this is to install Dart 2.17 and just see if it works.

[shilangyu]

It seems to be working well with dart 2.17