Skeleton-based animation

3D animation can be done either procedurally, or via attaching a skeleton to a 3D model. Adding support to the engine for skeleton-based animation is what most developers are used to.

https://en.wikipedia.org/wiki/Skeletal_animation

[skeleton_based_animation_structure.md](https://github.com/user-attachments/files/30911846/skeleton_based_animation_structure.md)

Acceptance Criteria:
- Design for class structure fits the current engine.
- A public facing interface implemented for the developers to use.
- Documentation published about how to programmatically add animators as ECS-components.

Follow up in the Editor:
- A design of a Animator-view, a way to animate objects "visually".
- A feature linked to this issue.
- A design for a Mixamo integration interface.