feat(secure_storage): add Swift Package Manager support to amplify_secure_storage

Migrate amplify_secure_storage iOS and macOS plugins to support Swift
Package Manager while maintaining backward compatibility with CocoaPods.

Changes:
- Add Package.swift for both iOS and macOS platforms
- Move sources from Classes/ to amplify_secure_storage/Sources/amplify_secure_storage/
- Move Obj-C public headers to include/amplify_secure_storage/ (iOS)
- Move PrivacyInfo.xcprivacy to SPM Sources directory
- Update podspec source_files and resource_bundles paths
- Update Pigeon swiftOut path for new directory structure
- Update Obj-C import path for relocated header
- Add .build/ and .swiftpm/ to .gitignore"

Author: ekjotmultani

.gitignore

@@ -43,6 +43,10 @@ amplify_outputs*.dart
 # Smithy
 .smithy.lsp.log
 
+# Swift Package Manager
+.build/
+.swiftpm/
+
 # Custom Actions output
 **/*.cjs.deps
 .flutter-plugins-dependencies

packages/secure_storage/amplify_secure_storage/example/.gitignore

@@ -5,9 +5,11 @@
 *.swp
 .DS_Store
 .atom/
+.build/
 .buildlog/
 .history
 .svn/
+.swiftpm/
 migrate_working_dir/
 
 # IntelliJ related

packages/secure_storage/amplify_secure_storage/example/ios/Flutter/AppFrameworkInfo.plist

@@ -7,6 +7,9 @@
 *.swp
 profile
 
+.build/
+.swiftpm/
+
 DerivedData/
 build/
 GeneratedPluginRegistrant.h
@@ -35,4 +38,4 @@ Icon?
 
 /Flutter/Generated.xcconfig
 /Flutter/ephemeral/
-/Flutter/flutter_export_environment.sh
+/Flutter/flutter_export_environment.sh

packages/secure_storage/amplify_secure_storage/example/ios/Runner.xcodeproj/project.pbxproj

@@ -13,12 +13,12 @@ A new Flutter plugin project.
   s.license          = { :file => '../LICENSE' }
   s.author           = { 'Your Company' => 'email@example.com' }
   s.source           = { :path => '.' }
-  s.source_files = 'Classes/**/*'
+  s.source_files = 'amplify_secure_storage/Sources/amplify_secure_storage/**/*.swift'
   s.dependency 'Flutter'
   s.platform = :ios, '13.0'
 
   # Flutter.framework does not contain a i386 slice.
   s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES', 'EXCLUDED_ARCHS[sdk=iphonesimulator*]' => 'i386' }
   s.swift_version = '5.9'
-  s.resource_bundles = {'amplify_secure_storage_privacy' => ['Resources/PrivacyInfo.xcprivacy']}
+  s.resource_bundles = {'amplify_secure_storage_privacy' => ['amplify_secure_storage/Sources/amplify_secure_storage/PrivacyInfo.xcprivacy']}
 end