All specialization constants are removed (they cause trouble in
WebGPU, since they don't support array sizing, and it was a pain
in Metal anyway) - they are now macro defined. WebGPU now runs, although
push constant emulation is not implemented yet.
Now it's even simpler, and it now generates multiple
shader languages at once! The copying mechanism is now
much simpler on non-mac platforms as well. HLSL is also now a supported shader target language.
* Now shader recompilation happens only when it needs to. Hurray for faster compiles!
* Changes to constructors for ShaderSource to make it more explicit.
* The version of SPIRV-Cross is updated, and now the glslang version pulled correctly matches what SPIRV-Cross needs. This fixes the annoying "cannot parse built-ins" bug.