Add DEPTH32FLOAT_STENCIL8 featue

[jinleili]

WebGPU spec: https://gpuweb.github.io/gpuweb/#depth32float-stencil8

Testing
Modified skybox locally and tested on metal, vulkan(--features=vulkan-portability) and dx12 backends:

const DEPTH_FORMAT = wgpu::TextureFormat::Depth32FloatStencil8;
fn required_features() -> wgpu::Features {
    wgpu::Features::DEPTH32FLOAT_STENCIL8
}

[cwfitzgerald]

One comment, otherwise lgtm.

[cwfitzgerald]

Thanks!