[ffi] Specifying external version, architecture and OS constraints

[dcharkes]

The Dart SDK tracking issue for:

• [native assets] Specify supported OS, Arch, minimum SDK version native#1500

Flutter has a way to specify the OS API version and supported architectures (the native build files), and supported OSes (pubspec). We don't have the same for Dart.

Being able to do so would help with both the native assets work as well with packages using dart:ffi without native assets that have version, architecture or OS constraints.

1. We could surface the info on pub.dev (Surface supported architectures per OS pub-dev#8010)
2. We could check before dart run, dart compile, dart build that the constraints are satisfied.

[dart-github-bot]

Summary: Dart currently lacks a mechanism to specify external version, architecture, and OS constraints for FFI packages. This limits the ability to manage native assets and ensure compatibility across different platforms.