Slang-RHI/WGPU: Invalid bind group layout entry used

[aleino-nv]

Affected tests:

• tests/bugs/buffer-swizzle-store.slang

Example output:

WGPU error: BindGroupLayoutEntry had none of buffer, sampler, texture, storageTexture, or externalTexture set
 - While validating entries[0]
 - While validating [BindGroupLayoutDescriptor]
 - While calling [Device].CreateBindGroupLayout([BindGroupLayoutDescriptor]).

[aleino-nv]

I found that Slang-RHI is leaving the 'access' field of WGPUStorageTextureBindingLayout undefined:
https://github.com/shader-slang/slang-rhi/blob/539322d79c1af13bbc5624a333b65a9e856a13a4/src/wgpu/wgpu-shader-object-layout.cpp#L183

The WebGPU spec contains a table, according to which read-write storage texture access is only allowed for r32uint, r32sint and r32float formats.

https://www.w3.org/TR/webgpu/#plain-color-formats

[aleino-nv]

Here is a PR that adds an explanation for WGPU, and adds a similar test that uses a structured buffer instead of a storage texture:
#5731

@csyonghe Do you think that's enough to close this issue?
There are lots of things we could do to improve slang-test/render-test/Slang-RHI, but I'd like to have a chat and discuss those options first.