Add Dynamic Subscriber Interface

[Fedik]

Summary of Changes

Current limitation of SubscriberInterface is that it does not allow to return listeners depend from runtime.
It has own pros and cons. However in CMS it is sometimes need to have a diffrenet listeners depend from the Application type.

I think DynamicSubscriberInterface will be a good for it.
The difference from SubscriberInterface is that it uses non-static method, which allows subscriber to configure listeners depending on runtime. Additionally, it supports callables.

Example it allows to use LazyServiceEventListener and protected callbacks,
which is not possible with SubscriberInterface :

public function getSubscribedEvents(): array
{
  $this->lazyListener = $this->lazyListener ?? new LazyServiceEventListener($container, $serviceId);
  $this->protectedListener = $this->protectedListener ?? function(Event $event) { ... };

  return [ 
    'onSomething' => $this->lazyListener,
    'onSomething2' => $this->protectedListener, 
  ];
}

The subscriber should implement only one of these interfaces, implementing both is not allowed (but we can discuss it of course).

Testing Instructions

Test is passes

Documentation Changes Required

New interfaces: DynamicSubscriberInterface and DispatcherDynamicSubscriberInterface.

[HLeithner]

I'm not a fan of this, at least in the cms I wouldn't like to have the overhead of dynamic loading on boot

[Fedik]

It not replacement, but an optional addittion when you need some kind of "private listeners".

This approach is much better than existing registerListeners and joomla/joomla-cms#43431 and joomla/joomla-cms#39387. Because it keep the Subscribber decoupled from Dispatcher.

This also allows to removeSubscriber() and "unload" the plugin, unlike other 2 approaches which is kind of "one way".