Add test to stress wide OpPhi instructions
New test that has a 1024 case wide OpPhi instruction.
The test has been written so that it is easy to change to any desirable
width; based on the SPIR-V specification a width of 16k should be
acceptable (as there can be 16k switch cases). However, that would
generate a rather large (about 50kLOC) shader.
Affects:
dEQP-VK.spirv_assembly.instruction.compute.opphi.wide
Components: Vulkan
VK-GL-CTS issue: 259
Change-Id: Ide349e19ab4811c8c8c13bff0d72ac6cf19349ed