Remove 16-bit storage from float16 vector tests

Remove 16-bit storage from float16 vector tests

Replace loads and stores of float16s with specialized function to
reinterpret as appropriate uints for vector extract dynamic, vector
insert dynamic and vector shuffle tests.

Component: Vulkan

VK-GL-CTS Issue: 1931

Affects:
dEQP-VK.spirv_assembly.instruction.*.float16.opvectorextractdynamic*
dEQP-VK.spirv_assembly.instruction.*.float16.opvectorinsertdynamic*
dEQP-VK.spirv_assembly.instruction.*.float16.opvectorshuffle*

Change-Id: I1757d2dc3dd8a45098b79ce519d26b351f298a00