[macOS] Add platform_channel sample/test (#123141)

Adds a macOS implementation of the platform_channel example,
demonstrating method channels and event channels with a battery power
plugin.

Adds platform_channel_sample_test_macos macOS host test to verify the
sample works.

Issue: flutter/flutter#79204

Author: cbracken

.ci.yaml

@@ -2972,6 +2972,20 @@ targets:
         ]
       task_name: platform_view_macos__start_up
 
+  - name: Mac platform_channel_sample_test_macos
+    bringup: true
+    recipe: devicelab/devicelab_drone
+    presubmit: false
+    timeout: 60
+    properties:
+      dependencies: >-
+        [
+          {"dependency": "xcode", "version": "14a5294e"}
+        ]
+      tags: >
+        ["devicelab", "hostonly", "mac"]
+      task_name: platform_channel_sample_test_macos
+
   - name: Mac plugin_dependencies_test
     recipe: devicelab/devicelab_drone
     timeout: 60

TESTOWNERS

@@ -250,6 +250,7 @@
 /dev/devicelab/bin/tasks/module_test.dart @zanderso @flutter/tool
 /dev/devicelab/bin/tasks/module_test_ios.dart @jmagman @flutter/tool
 /dev/devicelab/bin/tasks/native_ui_tests_macos.dart @cbracken @flutter/desktop
+/dev/devicelab/bin/tasks/platform_channel_sample_test_macos.dart @cbracken @flutter/desktop
 /dev/devicelab/bin/tasks/platform_channel_sample_test_windows.dart @cbracken @flutter/desktop
 /dev/devicelab/bin/tasks/platform_view_macos__start_up.dart @a-wallen @flutter/desktop
 /dev/devicelab/bin/tasks/platform_view_win_desktop__start_up.dart @yaakovschectman @flutter/desktop

dev/devicelab/bin/tasks/platform_channel_sample_test_macos.dart

@@ -0,0 +1,10 @@
+// Copyright 2014 The Flutter Authors. 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:flutter_devicelab/framework/framework.dart';
+import 'package:flutter_devicelab/tasks/integration_tests.dart';
+
+Future<void> main() async {
+  await task(createPlatformChannelSampleTest(deviceIdOverride: 'macos'));
+}

examples/platform_channel/macos/.gitignore

@@ -0,0 +1,7 @@
+# Flutter-related
+**/Flutter/ephemeral/
+**/Pods/
+
+# Xcode-related
+**/dgph
+**/xcuserdata/

examples/platform_channel/macos/Flutter/Flutter-Debug.xcconfig

@@ -0,0 +1 @@
+#include "ephemeral/Flutter-Generated.xcconfig"

examples/platform_channel/macos/Flutter/Flutter-Release.xcconfig

@@ -0,0 +1 @@
+#include "ephemeral/Flutter-Generated.xcconfig"