[front_end] Enable lint depend_on_referenced_packages

This would have caught a mistake I made in
https://dart-review.googlesource.com/c/sdk/+/447920.

Change-Id: I6a6a6964ce45648cdb0eec6ece68cb45913cd5fc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/447940
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>
Auto-Submit: Paul Berry <[email protected]>

Author: stereotype441

pkg/front_end/analysis_options.yaml

@@ -12,6 +12,7 @@ linter:
   rules:
     - collection_methods_unrelated_type
     - curly_braces_in_flow_control_structures
+    - depend_on_referenced_packages
     - prefer_adjacent_string_concatenation
     - unawaited_futures
     - avoid_void_async