Add Swift Package Manager support

Hello,

Flutter is migrating to [Swift Package Manager][]. Please [add Swift Package Manager support][] to your plugin.

Flutter will eventually deprecate and then remove support for CocoaPods. Adding Swift Package Manager support future-proofs your plugins.

[Swift Package Manager]: https://www.swift.org/documentation/package-manager/
[add Swift Package Manager support]: https://docs.flutter.dev/packages-and-plugins/swift-package-manager/for-plugin-authors#how-to-add-swift-package-manager-support-to-an-existing-flutter-plugin

### How to add Swift Package Manager support to your plugins

You can find the migration guide here: https://docs.flutter.dev/packages-and-plugins/swift-package-manager/for-plugin-authors#how-to-add-swift-package-manager-support-to-an-existing-flutter-plugin

If you run into issues or have questions, please reach out to the Flutter team. You can ping me at @loic-sharma, send a message to the #hackers-ios channel on [Flutter’s discord][], or [open a GitHub issue][].

Thank you for your wonderful contributions to the Flutter ecosystem!

[Flutter’s discord]: https://github.com/flutter/flutter/blob/master/docs/contributing/Chat.md
[open a GitHub issue]: https://github.com/flutter/flutter/issues/new/choose

### Why is Flutter migrating to Swift Package Manager?

[CocoaPods is now in maintenance mode][].

Swift Package Manager support is one of Flutter’s most requested features: [flutter#33850][].

Flutter's Swift Package Manager integration has several benefits:

1. **Access to the Swift package ecosystem**. Flutter plugins can use the growing ecosystem of [Swift packages][].
2. **Simplifies Flutter installation**. Swift Package Manager is bundled with Xcode. In the future, you won’t need to install Ruby and CocoaPods to target iOS or macOS.

[CocoaPods is now in maintenance mode]: https://blog.cocoapods.org/CocoaPods-Support-Plans/
[flutter#33850]: https://github.com/flutter/flutter/issues/33850
[Swift packages]: https://swiftpackageindex.com/

Start with Flutter’s migration guide linked in the issue, then inspect this plugin’s existing iOS and macOS package configuration to identify the integration points. Done means the plugin supports Swift Package Manager as described by the guide and its existing platform integrations continue to work.

Written by the indexing model from the issue text.