Shaders: rust-gpu integration to compile shader nodes to WGSL

[Firestar99]

Requires #3027

This PR adds the rust-gpu integration to compile shader nodes into a giant wgsl shader file (with multiple entry points). The runtime componentry to run these shaders can be found in #2985

From weekly updates

End of week update (week 11):

$ git checkout shaders
$ cargo b -p graphene-raster-nodes
    Finished `dev` profile [optimized + debuginfo] target(s) in 0.26s
$ ll ./target/spirv-builder/spirv-unknown-naga-wgsl/release/deps/graphene_raster_nodes.wgsl -h
-rw-r--r-- 1 firestar99 users 149K Aug  3 23:37 ./target/spirv-builder/spirv-unknown-naga-wgsl/release/deps/graphene_raster_nodes.wgsl

[timon-schelling]

I think it should be rust-gpu cargo b -r ... otherwise rustup will be used right? rust-gpu toolchain should not be available without wrapper script.

[Firestar99]

@timon-schelling I don't quite understand what you mean... could you attach that to some piece of code? Commit nix: use rustc_codegen_spirv.so from nix you made should contain the necessary switches to use the nix rust-gpu toolchain.

Resolved in voice call

[timon-schelling]

I'm getting

warning: dropping unsupported crate type `dylib` for target `wasm32-unknown-unknown`
warning: `graphene-raster-nodes` (lib) generated 1 warning

@TrueDoctor take a close look at the macro changes
otherwise LGTM

[Firestar99]

I can't fix that warning, that's the crate-type = [...] in grasternodes. rust-gpu needs dylib and you also want the default lib for CPU stuff and wasm. Technically, this makes you compile a dylib on CPU targets as well, so you'll get an *.so in your target. And wasm doesn't support that and emits this warning. But you can't config that per-target nor pass it as a cargo arg, so we're stuck with this for now.