chore: activate language strict rules

[dkrutskikh]

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix
[ ] New rule
[ ] Changes an existing rule
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[X] Other, please explain: active some rules
https://github.com/dart-lang/language/blob/master/resources/type-system/strict-raw-types.md
https://github.com/dart-lang/language/blob/master/resources/type-system/strict-inference.md

What changes did you make? (Give an overview)

Is there anything you'd like reviewers to focus on?

[codecov]

Codecov Report

Merging #601 (1e1e45b) into master (63e1b27) will increase coverage by 0.00%.
The diff coverage is 94.44%.

❗ Current head 1e1e45b differs from pull request most recent head e6030f0. Consider uploading reports for the commit e6030f0 to get more accurate results

@@           Coverage Diff           @@
##           master     #601   +/-   ##
=======================================
  Coverage   85.88%   85.88%           
=======================================
  Files         230      230           
  Lines        4894     4896    +2     
=======================================
+ Hits         4203     4205    +2     
  Misses        691      691           

Impacted Files	Coverage Δ
...ics/metrics_list/maintainability_index_metric.dart	100.00% <ø> (ø)
...rics/metrics_list/number_of_parameters_metric.dart	100.00% <ø> (ø)
...r/metrics/metrics_list/weight_of_class_metric.dart	100.00% <ø> (ø)
...zers/lint_analyzer/metrics/models/file_metric.dart	100.00% <ø> (ø)
...analyzers/lint_analyzer/metrics/models/metric.dart	100.00% <ø> (ø)
..._list/code_climate/lint_code_climate_reporter.dart	100.00% <ø> (ø)
...rs/reporters_list/github/lint_github_reporter.dart	100.00% <ø> (ø)
...orters/reporters_list/html/lint_html_reporter.dart	0.31% <ø> (ø)
lib/src/cli/commands/base_command.dart	67.30% <ø> (-1.22%)	⬇️
lib/src/analyzers/lint_analyzer/lint_analyzer.dart	93.75% <50.00%> (ø)
... and 15 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f1ad8e2...e6030f0. Read the comment docs.