Request Swift Package Manager adoption.

### Is there an existing issue for this? - [x] I have searched the existing issues ### Current Behavior This will become an error in a future version of Flutter. Please contact the plugin maintainers to request Swift Package Manager adoption. ### Expected Behavior This will become an error in a future version of Flutter. Please contact the plugin maintainers to request Swift Package Manager adoption. ### Steps with code example to reproduce <details> <summary>Steps with code example to reproduce</summary> ```dart // Paste your code here ``` </details> ### Stacktrace/Logs <details> <summary>Stacktrace/Logs</summary> ``` <Replace this line by pasting your stacktrace or logs here> ``` </details> ### Flutter version v3.44.0 ### Operating System, Device-specific and/or Tool ios 14 ### Plugin version ^5.14.3 ### Additional information _No response_ ### Self grab - [ ] I'm ready to work on this issue!