[3.x] Backport the new Tween system as SceneTreeTween

[timothyqiu]

Backports #41794 and later updates.

Like we have both Timer and SceneTreeTimer, the new Tween is backported as SceneTreeTween, so it does not break compatibility.

As it's expected to be created from get_tree().create_tween()/node.create_tween(), it does not matter what the class is called 😛

Some notes:

• interpolate_value() was recently changed to a static function on master, it's kept as a member function here.
• Callable is not available on 3.x, so this type of parameter is changed to a target and a method.
  • tween_callback() takes up to 8 additional args that'll be passed to the method.
  • tween_method() can only be called on methods that takes one parameter (Same as Tween.interpolate_method)
  • tween_callback() and tween_method() also takes an optional binds array for parameter binding.
• Only the TweenPauseMode enum is added, other enums uses Tween's version directly.
• scene/animation/easing_equations.h is copied from master.

[akien-mga]

scene/animation/easing_equations.h is copied from master.

3.x has it in thirdparty/misc/easing_equations.h, though possibly a bit different. This might need reworking so that the code that currently depends on thirdparty/misc/easing_equations.h switches to use scene/animation/easing_equations.h (or the other way around if compatible).

[timothyqiu]

I searched for the filename before copying, didn't expect it's a .cpp file on 3.x 🤣

thirdparty/misc/easing_equations.cpp is an unformatted version of easing_equations.h plus some Tween code. I kept easing_equations.h and moved those Tween code back to tween.cpp.

Like the enums, SceneTreeTween now uses the static Tween::run_equations() instead of its own version.

[Mickeon]

I've been writing the same boilerplate code so many times, I look forward to this being in 3.x as soon as possible! A nice way to ease the transition to this new way of doing Tweens.

[KoBeWi]

Awesome! I was thinking about doing this, but never got around to it.

tween_method() can only be called on methods that takes one parameter (Same as Tween.interpolate_method)

You could pass the binds as array. That's what 4.0 Tweens did originally before Callable.bind() was added.
Also for tween_callback(), you could pass binds as array too. It's consistent with connect() and doesn't have problems like not allowing null arguments.

(or the other way around if compatible).

4.0 easing equations work exactly the same, I just changed some code that could cause undefined behavior (e.g. #28177).

[KoBeWi]

Aside from the comment above, it should be fine now.
I'd also add a mention of SceneTreeTween somewhere to Tween.xml.

[akien-mga]

Thanks!

[KoBeWi]

This description is missing for some reason.
@timothyqiu