Try spec constants with more sizes and packing

Try spec constants with more sizes and packing

This commit adds new hand-tuned basic tests for specialization constants
using a wider variety of sizes and packing strategies for data in the
user data array, in order to check the implementation can correctly
extract values from it.

New tests:
dEQP-VK.pipeline.spec_constant.*int8*
dEQP-VK.pipeline.spec_constant.*int16*
dEQP-VK.pipeline.spec_constant.*int64*
dEQP-VK.pipeline.spec_constant.*float16*
dEQP-VK.pipeline.spec_constant.*_2
dEQP-VK.pipeline.spec_constant.*_packed
dEQP-VK.pipeline.spec_constant.*mixed*

Affected tests:
dEQP-VK.pipeline.spec_constant.*

Components: Vulkan
VK-GL-CTS issue: 2326

Change-Id: I94fc23d4c569edd38aa9e9e6c680a3353020d388