[SPIR-V] Putting NonWritable/NonReadable on the Struct instead of Variable

Description

When generating SPIR-V you will get something such as

OpMemberDecorate %block 0 Offset 0
OpMemberDecorate %block 0 NonWritable
OpDecorate %block Block
OpDecorate %var DescriptorSet 0
OpDecorate %var Binding 0

%runtime = OpTypeRuntimeArray %buffer_type
%block = OpTypeStruct %runtime
%ptr_sb = OpTypePointer StorageBuffer %block
%var = OpVariable %ptr_sb StorageBuffer

but ideally you should have the NonWritable on the OpVariable and not the OpTypeStruct

Discussed in the Vulkan Working Group and decided that the current generated SPIR-V from DXC is incorrect (working on spec-ing and getting spirv-val to help catch this)

Steps to Reproduce

The original shader can be found at https://github.com/KhronosGroup/Vulkan-ValidationLayers/issues/12100#issuecomment-4264326920

Actual Behavior

The SPIR-V should look similar to

OpDecorate %block Block
OpDecorate %var NonWritable
OpDecorate %var Binding 0
OpDecorate %var DescriptorSet 0

%runtime = OpTypeRuntimeArray %buffer_type    
%block = OpTypeStruct %runtime      
%ptr_sb = OpTypePointer StorageBuffer %buffer_type
%_var = OpVariable %ptr_sb StorageBuffer