Add test to stress wide OpPhi instructions

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