Show warning when plugins do not support SwiftPM (flutter#182506)

Provides a warning with a list of plugins that do not support SwiftPM.
This is displayed to the app developer. It then recommends they reach
out to the plugin maintainers to adopt SwiftPM.

Example:
```
The following plugins do not support Swift Package Manager for ios:
  - sqflite_sqlcipher
  - sign_in_with_apple
  - permission_handler_apple
  - flutter_secure_storage
  - flutter_inappwebview_ios
  - flutter_facebook_auth
  - flutter_contacts
  - flutter_config
  - fast_contacts
This will not be supported in a future version of Flutter. Please contact the plugin maintainers to request Swift Package Manager
adoption.
```

Fixes flutter#152038.

## Pre-launch Checklist

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there for submitting PRs.
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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.

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on [Discord].

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[Tree Hygiene]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
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Author: vashworth

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

@@ -148,6 +148,7 @@ class DarwinDependencyManagement {
     var pluginCount = 0;
     var swiftPackageCount = 0;
     var cocoapodCount = 0;
+    final Set<String> cocoapodOnlyPlugins = {};
     for (final Plugin plugin in _plugins) {
       if (plugin.platforms[platform.name] == null) {
         continue;
@@ -179,6 +180,10 @@ class DarwinDependencyManagement {
         cocoapodCount += 1;
       }
 
+      if (cocoaPodsCompatible && !swiftPackageManagerCompatible) {
+        cocoapodOnlyPlugins.add(plugin.name);
+      }
+
       // If not using Swift Package Manager and plugin does not have podspec
       // but does have a Package.swift, throw an error. Otherwise, it'll error
       // when it builds.
@@ -205,6 +210,15 @@ class DarwinDependencyManagement {
       }
     }
 
+    if (hostPlatformIsMacOS && cocoapodOnlyPlugins.isNotEmpty) {
+      _logger.printWarning(
+        'The following plugins do not support Swift Package Manager for ${platform.name}:\n'
+        '  - ${cocoapodOnlyPlugins.join('\n  - ')}\n'
+        'This will become an error in a future version of Flutter. Please contact the plugin '
+        'maintainers to request Swift Package Manager adoption.',
+      );
+    }
+
     // Only show warnings to remove CocoaPods if the project is using Swift
     // Package Manager, has already been migrated to have SPM integration, and
     // all plugins are Swift Packages.

packages/flutter_tools/test/general.shard/macos/darwin_dependency_management_test.dart

@@ -66,7 +66,16 @@ void main() {
               );
               await dependencyManagement.setUp(platform: platform);
               expect(swiftPackageManager.generated, isTrue);
-              expect(testLogger.warningText, isEmpty);
+              expect(
+                testLogger.warningText,
+                contains(
+                  'The following plugins do not support Swift Package Manager for '
+                  '${platform.name}:\n'
+                  '  - cocoapod_plugin_1\n'
+                  'This will become an error in a future version of Flutter. Please contact the '
+                  'plugin maintainers to request Swift Package Manager adoption.\n',
+                ),
+              );
               expect(testLogger.statusText, isEmpty);
               expect(cocoaPods.podfileSetup, isTrue);
               expect(
@@ -459,7 +468,10 @@ void main() {
               );
               await dependencyManagement.setUp(platform: platform);
               expect(swiftPackageManager.generated, isTrue);
-              expect(testLogger.warningText, isEmpty);
+              expect(
+                testLogger.warningText,
+                contains('The following plugins do not support Swift Package Manager'),
+              );
               expect(testLogger.statusText, isEmpty);
               expect(cocoaPods.podfileSetup, isTrue);
               expect(
@@ -526,7 +538,10 @@ void main() {
               );
               await dependencyManagement.setUp(platform: platform);
               expect(swiftPackageManager.generated, isTrue);
-              expect(testLogger.warningText, isEmpty);
+              expect(
+                testLogger.warningText,
+                contains('The following plugins do not support Swift Package Manager'),
+              );
               expect(testLogger.statusText, isEmpty);
               expect(cocoaPods.podfileSetup, isTrue);
               expect(
@@ -580,7 +595,10 @@ void main() {
               );
               await dependencyManagement.setUp(platform: platform);
               expect(swiftPackageManager.generated, isFalse);
-              expect(testLogger.warningText, isEmpty);
+              expect(
+                testLogger.warningText,
+                contains('The following plugins do not support Swift Package Manager'),
+              );
               expect(testLogger.statusText, isEmpty);
               expect(cocoaPods.podfileSetup, isTrue);
               expect(