NodeMaterial support in Loader

[Makio64]

Description

Add support to NodeMaterial in GltfLoader/Loader in general.

Solution

Assign node material directly instead of legacy material in Loaders.

Alternatives

Pass an option to the LoaderManager to return the node or legacy material version ( ex: StandardNodeMaterial / StandardMaterial) .
Then inside the loader we call this option to get the material class. This way the change can be effective for all loaders quite fast.

Additional context

From my understanding we're going to an all node material world in threejs.
In this sense it would be nice to directly got nodeMaterial when loading a 3d model.
I can open a PR if you think it's a good idea.