The SPIRV backend has a special type named `spirv.Image`. This type is
meant to correspond to the OpTypeImage instruction in SPIR-V, but there
is one difference. The access qualifier operand in OpTypeImage is
optional. On top of that, the access qualifiers are only valid for
kernels, and not for shaders.
We want to reuse this type when generating shader from HLSL, but we
can't use the access qualifier. This commit make the access qualifer
optional in the target extension type.
The same is done for `spirv.SampledImage`.
Contributes to #81036
