IShader, no more conversions, stage is now part of spec info.

[devshgraphicsprogramming]

Description

Remove unnecessary complexity of ICPUShader and IGPUShader.

Testing

All examples using shaders need to be tested.

TODO list:

• [x] require maintenance5 or graphics_pipeline_library
• [x] pass SPIR-V directly to pipeline creation without creating a VkShaderModule using maintenance5/graphics_pipeline_library pNext new API
• [ ] set debug object name on created graphics pipeline libraries
• [x] use SPIR-V Tools & Opt to create a copy of the SPIR-V, remove entry points not used by spec info, then run DCE and capability stripping pass