Add a way to clear/null all subscribers in AnimationPlayer events

[yosimba2000]

Going to be using C#.
Sometimes many subscribers are subscribed to the same event, and it's not convenient to remember each subscriber in order to unsubscribe them later on. Can we have a method that allows us to remove all subscribers at once? AFAIK, one easy way to do this is to set the Event equal to null, like this AnimationPlayer.AnimationFinished=null , but it's only possible from within the class that declared the Event. So to achieve this, a public method could be added inside the responsible class that sets the Event to null, and the method could therefore be called outside the class.

This can also be extended to all other events in Godot.