Update Samples for 3.16 (#2085)

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or adding, and why. Consider including before/after screenshots.*

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## Pre-launch Checklist

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experimental/web_dashboard/lib/src/widgets/category_chart.dart

@@ -2,7 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:charts_flutter/flutter.dart' as charts;
+import 'package:community_charts_flutter/community_charts_flutter.dart'
+    as charts;
 import 'package:flutter/material.dart';
 import 'package:intl/intl.dart' as intl;