RFC: Add ability for consumers to be notified of dispatched actions

[mrpmorris]

Some actions contain information that isn't destined for the store's state. For example, an effect that calls an API to return an editable object (e.g. Customer).

As the object is mutable it should not go into state where it can be modified. Instead, allow consumers to subscribe to the dispatching of actions so they can obtain a reference to the editable object for editing without it having to be reduced into state.

An example for observing dispatched actions in a component would look something like this

public class MyComponent : ComponentBase, IDisposable
{
	[Inject]
	protected IDispatcherObserver DispatcherObserver { get; set; }

	private IDisposable Subscription;

	protected override void OnInitialized()
	{
		base.OnInitialized();
		Subscription = DispatcherObserver.Observe<GetForUpdateResultAction>(SetModel);
		var getSupplierAction = new GetForUpdateAction(id: SupplierId);
		Dispatcher.Dispatch(getSupplierAction);
	}

	void IDisposable .Dispose()
	{
		Subscription?.Invoke();
	}
}

Or have a base Fluxor(some name)Component

protected override void OnInitialized()
{
    base.OnInitialized();
    Observe<GetForUpdateResultAction>(SetModel);
    var getSupplierAction = new GetForUpdateAction(id: SupplierId);
    Dispatcher.Dispatch(getSupplierAction);
}

private void SetModel(GetForUpdateResultAction action)
{
    Model = action.Supplier;
    StateHasChanged();
}