GLB Export

[deliciouslyevil]

Is your feature request related to a problem? Please describe.
The only exporter that is available is a VRML one, and WRL isn't a very well-supported format these days (even recent Blender versions don't support it by default). Adding GLB would be a great addition as it supports vertex color and is the standard for web viewers. It can also be embedded into PDFs and programs in the Microsoft ecosystem so would allow for embedding models into documentation, presentations, sharing on Teams. It would also allow us to pass our outputs from 3dmol.js into other 3D modeling software for further manipulation.

Describe the solution you'd like
exportGLB() that exports a GLB mesh of the current representation.