spirv-val: Improve Explicit Layout message

[spencer-lunarg]

closes #6323 and #6071

New messages now look like

[VUID-StandaloneSpirv-None-10684] Invalid explicit layout decorations on type for operand '5[%_ptr_Private__struct_2]', the Private storage class has a explicit layout from the Offset decoration.

and

[VUID-StandaloneSpirv-None-10684] Invalid explicit layout decorations on type for operand '6[%_ptr_Workgroup__arr_uint_uint_4]', the Workgroup storage class has a explicit layout from the ArrayStride decoration.

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Providing both the storage class and the decoration that makes it explicit layout should be enough, the whole details around which version make it valid or not-valid I think is overkill, the main thing is showing a SPIR-V generator what to look for

[spencer-lunarg]

@alan-baker friendly ping, mainly because I want to sneak this into the next SDK release and we are freezing the spirv commit friday

[alan-baker]

I think the shaderc smoketest is unrelated to your change.

[spencer-lunarg]

@alan-baker I can rebase incase and try again