Minor sample index cleanup (#1532)

web/samples_index/analysis_options.yaml

@@ -6,6 +6,7 @@ analyzer:
   language:
     strict-casts: true
     strict-inference: true
+    strict-raw-types: true
 
 linter:
   rules:
@@ -16,6 +17,11 @@ linter:
     directives_ordering: true
     package_api_docs: true
     package_prefixed_library_names: true
+    prefer_final_in_for_each: true
+    prefer_single_quotes: true
     test_types_in_equals: true
     throw_in_finally: true
+    unawaited_futures: true
     unnecessary_statements: true
+    use_enums: true
+    use_super_parameters: true