[HLSL] Support SPIR-V from HLSL for OpenGL

Sadly, but you can't currently use glslang to compile HLSL shaders for OpenGL right now.

Waiting forward for the moment when this will be finally available..

The issue provides no file, test, or entry point to follow. Start by reviewing the HLSL front end and SPIR-V generation paths described in the repository, then determine the required OpenGL support and its validation coverage. Done means HLSL shaders compile successfully to SPIR-V for OpenGL with appropriate tests.

Written by the indexing model from the issue text.