Stop using strong-mode options in dart2js_runtime_metrics and scrape

Change-Id: I89347335d14ecf539fc7ea7fc44bd31680dbc458
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/275302
Reviewed-by: Jake Macdonald <jakemac@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>

pkg/dart2js_runtime_metrics/analysis_options.yaml

@@ -2,5 +2,5 @@ analyzer:
   errors:
     import_internal_library: ignore
     export_internal_library: ignore
-  strong-mode:
-    implicit-casts: false
+  language:
+    strict-casts: true

pkg/scrape/analysis_options.yaml

@@ -1,6 +1,6 @@
 include: package:lints/recommended.yaml
 
 analyzer:
-  strong-mode:
-    implicit-casts: false
-    implicit-dynamic: false
+  language:
+    strict-casts: true
+    strict-raw-types: true