Add new tests for OpSConvert and OpFConvert

Add new tests for OpSConvert and OpFConvert

Added missing tests for OpSConvert and OpFConvert for compute and
graphics shaders.
Edited SPIR-V templates for OpSpecConstantOp-tests to support data types
other than int32 on tests where other types are required.

New tests:

dEQP-VK.spirv_assembly.instruction.compute.opspecconstantop.sconvert
dEQP-VK.spirv_assembly.instruction.compute.opspecconstantop.fconvert
dEQP-VK.spirv_assembly.instruction.graphics.opspecconstantop.sconvert*
dEQP-VK.spirv_assembly.instruction.graphics.opspecconstantop.fconvert*

Components: Vulkan

VK-GL-CTS issue: 711

Change-Id: Ia3cc3bc3f70f5216e364a2da4fb8fe78079fa445