Invoking an action no longer creates a new instance of the Action.

The LocalKey argument to the Intent constructor was removed.

The LocalKey argument to CallbackAction was removed.

The Action class is now a generic (Action<T extends Intent>) for better
type safety.

The OnInvokeCallback used by CallbackAction no longer takes a FocusNode
argument.

The ActionDispatcher.invokeAction signature has changed to not accept an
optional FocusNode, but instead take an optional BuildContext.

The LocalKey static constants (named key by convention) in Action
subclasses have been removed.

The Action.invoke and ActionDispatcher.invokeAction methods now return
the result of invoking the action as an Object.

The Action class may now be listened to for state changes.

The ActionFactory typedef has been removed, as it is no longer used.

Example analyzer failures