Add gltf converting for vctr

[tomlee-dev]

for VCTR (Polygon, Point)

for polyline, I am not yet done checking(I mean debug). I am pretty sure polyline processing is not working properly

and for Point. (has only one vertex, I thoght about this I haven't come up with better idea. I think it would be better to handle it appropriately depending on the engine.)

I don't have clear time line for Polyline (FYI)

spec document: https://github.com/CesiumGS/3d-tiles/tree/vctr/TileFormats/VectorData