analyzer_cli: switch to use strict-casts

Bug: https://github.com/dart-lang/sdk/issues/41651
Change-Id: I622210b0029325e52be2d8ef7dada1ceca961b6e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/222382
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>

pkg/analyzer_cli/analysis_options.yaml

@@ -1,9 +1,8 @@
 include: package:lints/recommended.yaml
 
 analyzer:
-  strong-mode:
-    implicit-casts: false
   language:
+    strict-casts: true
     strict-inference: true
   exclude:
     - test/data/**