WebGPURenderer: Simplify BindGroupLayout creation

[takahirox]

This PR simplifies BindGroupLayout Creation.

• GPURenderPipelineDescriptor seems to no longer take layout
  • https://gpuweb.github.io/gpuweb/#dictdef-gpurenderpipelinedescriptor
• We don't seem to no longer need to create bind group layout manually if we use pipeline.getBindGroupLayout()
  • getBindGroupLayout gpuweb/gpuweb#446
  • https://gpuweb.github.io/gpuweb/#pipeline-base

[Kangz]

That works, but note that if you plan to share bind groups between multiple pipelines, you'll have to revert to creating the layout explicitly, otherwise the layouts returned by getBindGroupLayout might not be the same.

[takahirox]

Thanks for the comment. I think Camera and Light parameters can be shared among objects (pipelines) in a scene. For example, we may create three groups camera (shared), lights (shared), and other pipeline specific parameters (non-shared). If we do that we may need to revert the change, or we may use hybrid (explicit layout creation for shared group while getBindGroupLayout for non-shared). Let's discuss when we optimize in the future.