3ds max custom attributes export issue

[AlexZhigin]

Hi @bghgary, @thomlucc, @SergioRZMasson, @FrogsInSpace!

I'm not sure if it's a bug or not, but the documentation says that the custom attributes of all nodes are exported. But it doesn't happen in case of pointhelpers, bones and dummies.

https://doc.babylonjs.com/features/featuresDeepDive/Exporters/3DSMax_to_glTF/#custom-attributes

1. Added custom attributes on ‘Door_Link’ pointhelper and ‘Door_Geo’ geometry:
   
   

2. When exporting glb, you can already see in the log that custom parameters are only added for mesh:
   

3. In the babylonjs sandbox, you can also see that only geometry has custom attributes:

A scene from screenshots (2020 version):
https://drive.google.com/file/d/1mBIj4ymhzLTB9r2DPFFQyo-slVcUUFFE/view?usp=sharing

If this is not a bug, then my huge request №1 is to add the ability to export custom attributes for point helpers and/or dummies.

And a huge request №2:
Add the ability to export custom attributes of the following type:

  "extras" : {
    "myParam" :  [
      0,
      1,
      0
    ]
  }

I would like to suggest the following method of export:

I'm sorry, but I simply cannot understand this solution..

..and I suggest exporting all the array values instead of the index of one of the values.

[bghgary]

This project is in maintenance mode, but we do take external contributions. Hopefully someone from the community will be willing to implement this.