Implement SPV_KHR_subgroup_vote

Implement SPV_KHR_subgroup_vote

doc.cpp: Add capabilities, scope to the opcodes. Add opcode and
capability strings.
GLSL.ext.KHR.h: Add extension
string.
GlslangToSpv.cpp: Fix handling of opcodes to generate
appropriate SPIR-V.
spirv.hpp: Add capability and opcode
enums.
spv.shaderGroupVote.comp.out: Update SPIR-V output for test
shader.