[build_actor] Add skeleton and animation support

[water111]

This adds a feature to build_actor to support importing skeletons and animations from .glb files.

Multiple animations are handled and will use the name in the GLB. The default viewer process will end up playing back the first animation.

There are a few limitations:

• You can only have around 100 bones. It is technically possibly to have slightly more, but certain animations may fail to compress when there are more than ~100 bones.
• Currently, all animations have 60 keyframes per second. This is a higher quality than what is normally used. If animation size becomes problematic, we could make this customizable somehow.
• There is no support for the align bone.