[objective_c] Move to a non-labs publisher

[stuartmorgan-g]

Filing for tracking. Before we switch any flutter/packages plugins to use ffigen for iOS/macOS, objective_c should ideally be on a non-labs publisher. For example, path_provider_foundation would be a good candidate for an FFI implementation (I have an implementation essentially ready), but path_provider is a foundational plugin in the Flutter ecosystem, so it shouldn't have a runtime dependency on a package that is still in an experimental stage.

[dcharkes]

cc @goderbauer

[liamappelbe]

I have another major version bump planned for package:objective_c. After that I plan to move it to the dart.dev publisher. Ffigen is already in tools.dart.dev.

[zeyus]

What about code_assets, native_toolchain_c and hooks I would love for my package to not have to use experimental packages, and currently it is still required to use the main channel.

[stuartmorgan-g]

None of those packages are required by currently-planned flutter/packages work, so would best be discussed in a new issue describing the use case.