In GLSL, 8-bit types require GL_EXT_shader_8bit_storage. 16-bit types
can use either GL_AMD_gpu_shader_int16/GL_AMD_gpu_shader_half_float or
GL_EXT_shader_16bit_storage.
A lot of changes in spirv-opt output.
Some new invalid SPIR-V was found but most of them were not significant
for SPIRV-Cross, so just marked them as invalid.