Fixup `experimental/federated_plugin` (#1776)

Replaces https://github.com/flutter/samples/pull/1749

FYI @negotoyolo

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[CLA]: https://cla.developers.google.com/
[Discord]: https://github.com/flutter/flutter/wiki/Chat
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md

experimental/federated_plugin/federated_plugin/example/test/widget_test.dart

@@ -10,15 +10,17 @@ import 'package:flutter_test/flutter_test.dart';
 void main() {
   group('federated plugin demo tests', () {
     const batteryLevel = 45;
-    setUpAll(() {
+
-      const MethodChannel('battery').setMockMethodCallHandler((call) async {
+    testWidgets('get current battery level from platform', (tester) async {
+      tester.binding.defaultBinaryMessenger.setMockMethodCallHandler(
+        const MethodChannel('battery'),
+        (call) async {
           if (call.method == 'getBatteryLevel') {
             return batteryLevel;
           }
-      });
+          return 0;
-    });
+        },
-
+      );
-    testWidgets('get current battery level from platform', (tester) async {
       await tester.pumpWidget(const MyApp());
 
       // Tap button to retrieve current battery level from platform.

experimental/federated_plugin/federated_plugin/test/federated_plugin_test.dart

@@ -11,13 +11,17 @@ void main() {
 
   group('Federated Plugin Test', () {
     const batteryLevel = 34;
-    const MethodChannel('battery').setMockMethodCallHandler((call) async {
+
+    testWidgets('getBatteryLevel method test', (tester) async {
+      tester.binding.defaultBinaryMessenger.setMockMethodCallHandler(
+        const MethodChannel('battery'),
+        (call) async {
           if (call.method == 'getBatteryLevel') {
             return batteryLevel;
           }
-    });
+          return 0;
-
+        },
-    test('getBatteryLevel method test', () async {
+      );
       final result = await getBatteryLevel();
       expect(result, batteryLevel);
     });

experimental/federated_plugin/federated_plugin_platform_interface/test/federated_plugin_platform_interface_test.dart

@@ -11,13 +11,17 @@ void main() {
 
   group('MethodChannel test', () {
     const batteryLevel = 89;
-    const MethodChannel('battery').setMockMethodCallHandler((call) async {
+
+    testWidgets('getBatteryLevel method test', (tester) async {
+      tester.binding.defaultBinaryMessenger.setMockMethodCallHandler(
+        const MethodChannel('battery'),
+        (call) async {
           if (call.method == 'getBatteryLevel') {
             return batteryLevel;
           }
-    });
+          return 0;
-
+        },
-    test('getBatteryLevel method test', () async {
+      );
       final locationMethodChannel = BatteryMethodChannel();
       final result = await locationMethodChannel.getBatteryLevel();
       expect(result, batteryLevel);

tool/flutter_ci_script_beta.sh

@@ -26,13 +26,10 @@ declare -ar PROJECT_NAMES=(
     "desktop_photo_search/material"
     "experimental/context_menus"
     "experimental/element_embedding_demo"
-    # TODO(DomesticMouse): 'setMockMethodCallHandler' is deprecated and shouldn't be used.
+    "experimental/federated_plugin/federated_plugin"
-    # "experimental/federated_plugin/federated_plugin"
+    "experimental/federated_plugin/federated_plugin/example"
-    # TODO(DomesticMouse): 'setMockMethodCallHandler' is deprecated and shouldn't be used.
-    # "experimental/federated_plugin/federated_plugin/example"
     "experimental/federated_plugin/federated_plugin_macos"
-    # TODO(DomesticMouse): 'setMockMethodCallHandler' is deprecated and shouldn't be used.
+    "experimental/federated_plugin/federated_plugin_platform_interface"
-    # "experimental/federated_plugin/federated_plugin_platform_interface"
     "experimental/federated_plugin/federated_plugin_web"
     "experimental/federated_plugin/federated_plugin_windows"
     "experimental/linting_tool"

tool/flutter_ci_script_master.sh

@@ -27,13 +27,10 @@ declare -ar PROJECT_NAMES=(
     # TODO(DomesticMouse): The function can't be unconditionally invoked because it can be 'null'.
     # "experimental/context_menus"
     "experimental/element_embedding_demo"
-    # TODO(DomesticMouse): 'setMockMethodCallHandler' is deprecated and shouldn't be used.
+    "experimental/federated_plugin/federated_plugin"
-    # "experimental/federated_plugin/federated_plugin"
+    "experimental/federated_plugin/federated_plugin/example"
-    # TODO(DomesticMouse): 'setMockMethodCallHandler' is deprecated and shouldn't be used.
-    # "experimental/federated_plugin/federated_plugin/example"
     "experimental/federated_plugin/federated_plugin_macos"
-    # TODO(DomesticMouse): 'setMockMethodCallHandler' is deprecated and shouldn't be used.
+    "experimental/federated_plugin/federated_plugin_platform_interface"
-    # "experimental/federated_plugin/federated_plugin_platform_interface"
     "experimental/federated_plugin/federated_plugin_web"
     "experimental/federated_plugin/federated_plugin_windows"
     "experimental/linting_tool"