Update FBXLoader

[takahirox]

This PR updates FBXLoader

• Seems like FBX can include unused materials which don't have any connections. Let's ignore them so far. This fixes FBXLoader failure #11973 loading failure issue
• Switches default material from basic to standard. standard material is more 'standard' than basic material in Three.js now

[WestLangley]

Switches default material from basic to standard

Here's the thing... MeshStandardMaterial is designed to be used with an environment map so there is something to reflect. If there is no environment map, MeshPhongMaterial is likely better. If there is no indication of material shininess, then MeshLambertMaterial is preferable. All of these options assume lights in the scene.

But this is a judgement call... I would probably default to Lambert.

[takahirox]

The reason why I chose Standard is I saw a FBX file which includes materials the shader type of which are 'unknown' but look like PBR based materials (they have envMap, roughness, and others).

Of course, it'd be a minor case and I don't have any special preference.
If Lambert would be better, I'll change.

[mrdoob]

Lets hope people use environment maps when using FBXLoader 😉

[mrdoob]

Thanks!