Re-add Craig Labenz's code sharing sample (#1466)

* Revert "Revert "Add code sharing sample (#1444)" (#1464)"

This reverts commit dc50c46ef1.

* Opting out failing tests on Windows for CI

Co-authored-by: Craig Labenz <craig.labenz@gmail.com>

code_sharing/client/test/widget_test.dart

@@ -0,0 +1,15 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:client/main.dart';
+
+void main() {
+  group('App should', () {
+    testWidgets('build its widgets', (WidgetTester tester) async {
+      await tester.pumpWidget(
+        MyApp(
+          getCount: () => Future.value(1),
+          increment: (int x) => Future.value(x),
+        ),
+      );
+    });
+  });
+}