Outdated "How does it work" tutorial about Input Events

[Sauermann]

The tutorial "How does it work" about Input Events
https://docs.godotengine.org/en/stable/tutorials/inputs/inputevent.html#how-does-it-work
diverges in many details from the current implementation.

I suggest to add a warning to this chapter, so that inexperienced users are made aware of the fact that not all information within this chapter is up to date.

I am aware of the following aspects, where the tutorial diverges from the actual implementation:

• Unexpected InputEvent delivery order in 2D scene with ViewportContainer godot#25525
• _unhandled_key_input method missing from documentation #2581
• The InputEvent graph is outdated #2619
• viewports and their children usually never receive input events
• in some cases parents receive input events before their children (ViewportContainer related)
• in some cases the root node never receives an _gui_input event, although all Control-children have their mouse_filter set to "pass" (ViewportContainer related)
• in some cases a key triggers an _unhandled_key_input() event for a node and afterwards triggers an _unhandled_input() event for a different node (ViewportContainer related)

As an example, here is an actual order of _input key-events (Godot V3.2.1):