Add missing SConvert, FConvert and UConvert tests

Add missing SConvert, FConvert and UConvert tests

Different variations of SConvert, FConvert and UConvert weren't properly
tested in compute and graphics shaders.

Affects:

dEQP-VK.spirv_assembly.instruction.compute.sconvert.*
dEQP-VK.spirv_assembly.instruction.compute.uconvert.*

New tests:

dEQP-VK.spirv_assembly.instruction.compute.sconvert.int32_to_*int16
dEQP-VK.spirv_assembly.instruction.compute.sconvert.int64_to_*
dEQP-VK.spirv_assembly.instruction.compute.sconvert.uint*
dEQP-VK.spirv_assembly.instruction.compute.sconvert.*vec*
dEQP-VK.spirv_assembly.instruction.compute.uconvert.uint32_to_uint16
dEQP-VK.spirv_assembly.instruction.compute.uconvert.uint64_to_*
dEQP-VK.spirv_assembly.instruction.compute.fconvert.*
dEQP-VK.spirv_assembly.instruction.graphics.sconvert.*
dEQP-VK.spirv_assembly.instruction.graphics.uconvert.*
dEQP-VK.spirv_assembly.instruction.graphics.fconvert.*

Components: Vulkan

VK-GL-CTS issue: 880

Change-Id: Id84c7a20749cd15e84a9c85993c1e6574712889e