Dynamically register events to dispatch

[sambostock]

Note

This draft PR is a companion to Shopify/ruby-lsp#3291, which proposes this approach. Tests and other things have been omitted for now in the interest of getting feedback on the approach first, and will be added if we decide to move forward.

Instead of requiring the consumer to provide a list of all events which they wish to handle, we can give them to option of dynamically detecting them, by scanning the listener's public methods.

This approach is similar to that used by Minitest (scanning for test_ methods) and Rails generators (running all public methods in the order they are defined).

While this is slower than specifying a hard coded list, the penalty is only during registration. There is no change the the behaviour of dispatching the events. It is also a non-breaking change, so consumers can continue specifying each event if desired.

[kddnewton]

I would rather have a separate method for this, as this behavior gets magically triggered by having no events in the list currently. Something like:

def register(listener, *events)
  events.each { |event| (listeners[event] ||= []) << listener }
end

def register_public_methods(listener)
  register(listener, *listener.public_methods(false).grep(/^on_.*_(enter|leave)$/))
end

The other difference I would like to see I have in the example here, which is that I think we should not include inherited methods, (so using public_methods(false)).