[flutter] compilation errors with the release of flutter 3.16.0

[erickzanardo]

With the release of Flutter 3.16.0 which happened yesterday (November 15th, 2023), some compilation errors were introduced in the raw_image_provider package, used by the flutter runtime, which make the the spine_flutter package not work in this new flutter version.

I've already submitted a PR to the raw_image_provider package: yrom/flutter_raw_image_provider#1

If that PR gets merged, I am happy to open a PR here to update the dependency, but I am opening this issue here so it can be tracked here as well.

[badlogic]

Thank you!

[badlogic]

Since the author is not reactive to your pull request, I've included the dependency directly in source form in spine-flutter.

I've also bumped our minimum Flutter SDK target version up to 3.16.0 and released new packages to pub.dev.

[erickzanardo]

Thanks!!!