Improve Shadertoy Utility

[Vipitis]

picking up from #360

Several steps to this PR (will be updated)

• add offscreen support
• add snapshot method
• validate shadercode (with naga?) before creating shader module (addressed by allow handling errors for spirv and glsl shader gfx-rs/wgpu-native#313)
• add tests for new features
• fix style
• rebase

I welcome any feedback to my additions. I don't want to break any existing functionality.

[Vipitis]

short update, I had encountered more panics and found a ways to catch them by doing more translations.
And now that glsl errors get handled properly, it really shouldn't be here anymore.

Would it be okay to take all of that validation out (I will keep it in own project instead) and just add the offscreen and snapshot features with this PR for now?

[almarklein]

Would it be okay to take all of that validation out (I will keep it in own project instead) and just add the offscreen and snapshot features with this PR for now?

Yes, that sounds good! The glsl validation are present in the latest wgpu-native release, so they will be in wgpu-py in the next update.

[almarklein]

Thanks!