webGPU support

[F3der1co]

WGSL effect variants added and allowing concatenation.
Warning if an effect does not have a WGSL variant.

[skymen]

Currently this only supports WebGL shaders with a single variant. Supporting shaders that have WebGL2 or WGSL variants is going to take some time, since both require an entirely new token parser and code generator.

I don't know if one exists for WebGL 2 and given that WGSL is so new, I don't think one exists for it yet.
For now, it might be a bit hard to add support for these two