update<T> method
Updates the value of the state referenced by ref
with a function which
provides the current state.
An optional action
can be send to track which method did the update.
Implementation
@protected
@nonVirtual
void update<T>(StateRef<T> ref, Updater<T> updater, [Object? action]) {
scope.write(ref, updater(scope.read(ref, null)), action);
}