WebGPU Support

Hey, it seems like Shapes doesn't support the new WebGPU rendering backend. There are lots of errors about redefinitions when the project is built that I'm just not savvy enough with shaders to parse. I appreciate that WebGPU support is currently experimental so not many people are using it 😊 happens for all render pipelines, reproduction steps:

1. blank project in unity 6.1 or above
2. web build profile
3. Enable the WebGPU API (and remove the WebGL fallback)
4. Build