[try-slang]: we need to support write-only texture for wgsl

[kaizhangNV]

Currently slang only have read-only and read-write texture support. That will make it hard to work with WebGPU, because it means that we can only use very limited texture format in the shader for storage binding.

here is the list for the access of each texture format: https://www.w3.org/TR/webgpu/#texture-format-caps