disallow equivalent of Vulkan's vertexPipelineStoresAndAtomics

[dneto0]

To reach the broadest set of devices, WebGPU won't assume that the target supports the Vulkan feature bit vertexPipelineStoresAndAtomics. E.g. SSBOs in a vertex shader should be marked readonly in GLSL (or equivalent in SPIR-V)

Thanks @sarahM0 for flushing this out.

[litherum]

WHLSL likely needs to do this too.