replaced splat api with class based library

[lpalombo]

This is the implementation I've been working on. It's a little closer to something the Three.js implementers would accept.

• It uses a FileLoader as opposed to fetch to integrate with the LoadingManager class for more easily keeping track of assets that are loaded
• All methods related the splat object are kept in the GaussianSplatObject class. It could probably also extend an Object3D/Mesh to avoid the object.mesh stuff in the <Splat> component. The end user also doesn't need to keep track of any methods in a frameloop either.
• cloning is currently broken. You can only show one url at a time, but we could probably extend the .clone method and use the drei component, similar to GLTFs
• added a sample TaaPass component if you want to play with it.