When iOS and macOS Flutter apps build, they use Xcode Run Scripts to call do various logic.

For iOS, the Run Scripts calls a bash file (xcode_backend.sh), which then calls a dart file (xcode_backend.dart). xcode_backend.dart then calls flutter assemble.

For macOS, the Run Scripts calls a bash file (macos_assemble.sh), which then calls flutter assemble directly.

xcode_backend.dart and macos_assemble.sh do roughly the same thing. We should call xcode_backend.dart from macos_assemble.sh like we do in xcode_backend.sh so logic can be shared and written in Dart. Since these files all live within the tool, no changes to the project will be needed.

This will simplify adding shared logic for SwiftPM: flutter.dev/go/swift-package-manager-plugins-v3