LWOLoader: dev branch factorization

[sciecode]

This PR intends to return LWO main development branch to three.js and extend a factorization scheme per discussed on threejs/lwoloader#24

It does not include update to typescript definition per module import, which I think might be necessary. If it is, I would like to request help from someone more familiar with it, as my version would likely be useless.

discussion
I would like to just briefly discuss my opinion on the failed approach of trying to maintain a separated dev repository from Three.js. Having an autonomous control of development is beneficial, but having to keep both Three.js version and Dev branch files synchronized proved to be a bigger burden.

If we were to try a similar approach for other loaders in the future, I would strongly recommend using git submodule approach where the entire development is also moved to a different repository.

[sciecode]

https://rawcdn.githack.com/sciecode/three.js/fad42e6be39949b2ebc2b27878fcc8eabe21f4eb/examples/webgl_loader_lwo.html

[mrdoob]

Thanks!

[mrdoob]

If we were to try a similar approach for other loaders in the future, I would strongly recommend using git submodule approach where the entire development is also moved to a different repository.

One downside of submodules is that when you download the repo as a zip file submodules are not included. Or at least that used to be the case years ago.

[looeee]

git clone --recurse-submodules will clone with submodules. But I don't think there's any way to download them in the zip.

Here are the previous discussion related to the LWOLoader being in a separate repo:
#16679 #16678