Fix hardcoded reference to material[ 0 ] with currentMaterialSlot

Fixes to Maya exporter

- Export materials before meshes, so they can be applied to faces.
- Raise an error on faces with > 4 vertices instead of writing JSON
  which will fail to load.
- Correctly export transparency -- black in Maya means opaque.

Updated layers doc to remove reference to masks

Examples: Clean up

Fixed display dashed lines in SVG renderer #11879

make DOF work again.

Correct Layers doc typo.

The documentation says objects start out on layer 1, but as far as I can tell, an object's layers are initialized to layer 0, which corresponds to a mask of `1`, perhaps the source of the confusion?

GLTF2Loader: Improved error handling.

3DSLoader - Fixed UV warnings and calculate OBJ origin position

Add multi material per object support to the Editor.

paramThreeToGL made public

XLoader: Fix parameter and clean up example

[gltf] Use flat shading if normals are not included.