Bringing back the in-editor Bone/IK tool

[poohcom1]

In Godot 3.x, there's a in-editor Bone tool that allows nodes to be manipulated with IK within the editor itself.

As far as I'm aware, this feature was removed in 4.0 as it was supposed to be replaced with the improved Skeleton2D IK tools as mentioned in this PR: godotengine/godot#47872.

However, I felt like this wasn't necessary, as they weren't really doing the same thing.

• The in-editor bones is useful for creating cutout animation that isn't meant to be interactive in runtime. This allows animators to easily create frame-by-frame animations within the Godot engine itself, without restricting nodes into a simulation.
• The new Skeleton2D IK system is meant for procedural animation and/or physics simulation.

I think the new and improved IK system is absolutely awesome, but I don't think its a replacement for the editor bone tool. As someone who does a lot of traditional animation rather then procedural animation, setting up a Skeleton2D is an overkill for my use case and I would prefer to also have the option of using in-editor bones.

Anyway, I wanted to discuss this as it seems like no one really misses this feature other than me, so maybe the removal was warranted. My issues is that there didn't seem to be any clear reasons for its removal, so I'm curious if there are others who noticed it. Any opinions on the topic would be appreciated.