Blended/Masked materials don't work on Apple Vision Pro

[atteneder]

glTFast uses a single shader graph for all sorts of surface types (opaque, transparent, alpha clipped) by setting certain keywords/properties at runtime. This does not work with Polyspatial visionOS, as the shader graphs are converted to MaterialX at build time.

The only solution that comes to mind and has proven to work is to duplicate the shader graph per surface type and use varying shader graphs, depending on the material. Needless to say, this multiplies the maintenance effort in the long run.

See discussion in #666 for origin details and a user-provided solution.