Move joystick-axis-to-button simulation out of JoystickHandler

[Susko3]

This will allow AndroidJoystickHandler (coming soon) to reuse this logic without code duplication.
Inheritance is not an option as AndroidInputHandler is used on Android.

This code does look a bit dubious as JoystickButtonInput.Apply is called within JoystickAxisInput.Apply, but the current order of events is preserved.

KeyCombination does have a similar scroll delta to button conversion, but putting the logic there will break existing JoystickButton.JoystickAxisN usages.

[peppy]

Does this mean the android joystick handler will need to have its own implementation of the deadzone?

[Susko3]

I plan to make rescaleByDeadzone internal static to reuse the logic.

[frenzibyte]

I'm not really sure about the existence of "joystick axis buttons" instead of KeyBindingContainer-level ones, but I suppose this is fine for now.