[objective_c] Implement Swift Package Manager support for the objective_c plugin

[electricbolt]

Please implement Swift Package Manager support for the objective_c plugin as documented here: https://docs.flutter.dev/packages-and-plugins/swift-package-manager/for-plugin-authors
(cocoapods is deprecated).

[dcharkes]

We're migrating the package to be a Dart package with build hook rather than a plugin

• [objective_c] Publish v9.2.0 #2815

Could you try using a git-dependency on the unpublished versions to see if this solves your problem? (Hopefully we'll publish today/tomorrow.)

[electricbolt]

Thanks, that appears to work. I'll leave this ticket open until you publish objective_c 9.2.0, then I'll test again.

[electricbolt]

Working great thanks.