[tool] Add a telemetry event to track SwiftPM migration (flutter#166773)

Flutter is migrating from CocoaPods to Swift Package Manager to manage
native dependencies on iOS and macOS. We'd like to answer the following
questions:

1. Can we remove CocoaPods support from Flutter's tooling?
2. Can we tell plugin authors that they can remove CocoaPods integration
from their plugins?

This makes the Flutter tool send an event when it injects plugins into
an iOS or macOS project. This will happen whenever a user does commands
like `flutter build ios`, `flutter build macos`, and more.

Part of flutter#147602

Depends on: dart-lang/tools#2062

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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

<!-- Links -->
[Contributor Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview
[Tree Hygiene]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
[test-exempt]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md
[Features we expect every widget to implement]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes
[Discord]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md
[Data Driven Fixes]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

Author: loic-sharma

packages/flutter_tools/lib/src/flutter_plugins.dart

@@ -1327,7 +1327,9 @@ Future<void> injectPlugins(
             templateRenderer: globals.templateRenderer,
           ),
           fileSystem: globals.fs,
+          featureFlags: featureFlags,
           logger: globals.logger,
+          analytics: globals.analytics,
         );
     if (iosPlatform) {
       await darwinDependencyManagerSetup.setUp(platform: SupportedPlatform.ios);

packages/flutter_tools/lib/src/macos/darwin_dependency_management.dart

@@ -2,9 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:unified_analytics/unified_analytics.dart';
+
 import '../base/common.dart';
 import '../base/file_system.dart';
 import '../base/logger.dart';
+import '../features.dart';
 import '../plugins.dart';
 import '../project.dart';
 import 'cocoapods.dart';
@@ -21,20 +24,26 @@ class DarwinDependencyManagement {
     required CocoaPods cocoapods,
     required SwiftPackageManager swiftPackageManager,
     required FileSystem fileSystem,
+    required FeatureFlags featureFlags,
     required Logger logger,
+    required Analytics analytics,
   }) : _project = project,
        _plugins = plugins,
        _cocoapods = cocoapods,
        _swiftPackageManager = swiftPackageManager,
        _fileSystem = fileSystem,
-       _logger = logger;
+       _featureFlags = featureFlags,
+       _logger = logger,
+       _analytics = analytics;
 
   final FlutterProject _project;
   final List<Plugin> _plugins;
   final CocoaPods _cocoapods;
   final SwiftPackageManager _swiftPackageManager;
   final FileSystem _fileSystem;
+  final FeatureFlags _featureFlags;
   final Logger _logger;
+  final Analytics _analytics;
 
   /// Generates/updates required files and project settings for Darwin
   /// Dependency Managers (CocoaPods and Swift Package Manager). Projects may
@@ -87,6 +96,7 @@ class DarwinDependencyManagement {
       // whether to run.
       useCocoapods = _plugins.isNotEmpty;
     }
+
     if (useCocoapods) {
       await _cocoapods.setupPodfile(xcodeProject);
     }
@@ -95,6 +105,21 @@ class DarwinDependencyManagement {
     else if (xcodeProject.podfile.existsSync() && xcodeProject.podfileLock.existsSync()) {
       _cocoapods.addPodsDependencyToFlutterXcconfig(xcodeProject);
     }
+
+    final Event event = Event.flutterInjectDarwinPlugins(
+      platform: platform.name,
+      isModule: _project.isModule,
+      swiftPackageManagerUsable: xcodeProject.usesSwiftPackageManager,
+      swiftPackageManagerFeatureEnabled: _featureFlags.isSwiftPackageManagerEnabled,
+      projectDisabledSwiftPackageManager: _project.manifest.disabledSwiftPackageManager,
+      projectHasSwiftPackageManagerIntegration:
+          xcodeProject.flutterPluginSwiftPackageInProjectSettings,
+      pluginCount: totalCount,
+      swiftPackageCount: swiftPackageCount,
+      podCount: podCount,
+    );
+
+    _analytics.send(event);
   }
 
   /// Returns count of total number of plugins, number of Swift Package Manager