Feature's should auto-disable if their dependencies are disabled.

[ahammer]

in DartBoardFeature there is an "enabled" flag, that allows a feature to turn off. E.g. Firebase only works across Android/iOS/MacOS/Web. So I wouldn't want to enable the feature on unsupported platforms.

Currently the solution would be to set "enabled" to a platform check like

  @override
  bool get enabled => kIsWeb || Platform.isAndroid || Platform.isIOS;

You can also disable features manually by calling setFeatureImplementation(featureName, null)

As a framework user, I'd like for a disabled feature to automatically propagate across the feature tree.

E.g. at Feature Linking, prune the tree of implicitly disabled features, whether that be a feature that is explicitly disabled (e.g. with setFeatureImplementation to null, or it's implicitly disabled because of a call to enabled.

Acceptance:

• Be able to disable a high level feature (e.g. redux), observe dependent features being removed (e.g. Minesweeper).
• Be able to disable features via enabled check, e.g. platform check. And propagate that to dependent features. E.g. FirebaseAuth, FirebaseDatabase should disable on Windows/Linux, and features that use them shouldn't be presented (e.g. Chat).