Compile each static shader using shaderc to Spir-V binaries.
The main goal is to make sure that the GLSL created using ShaderCreateInfo and able to compile to Spir-V.
For the second stage a correct pipeline needs to be created and some shader would need more
adjustments (push constants size).
With this patch future changes to GLSL sources can already be checked against vulkan, without the
backend finished.
Mechanism has been tested using MacOS and MoltenVK. For other OS, we should finetune CMake
files to find the right location to shaderc.
```
************************************************************
*** Build Mon 12 Dec 2022 11:08:07 CET
************************************************************
Shader Test compilation result: 463 / 463 passed (skipped 118 for compatibility reasons)
OpenGL backend shader compilation succeeded.
Shader Test compilation result: 529 / 529 passed (skipped 52 for compatibility reasons)
Vulkan backend shader compilation succeeded.
```
Reviewed By: fclem
Maniphest Tasks: T102760
Differential Revision: https://developer.blender.org/D16610
This patch adds a placeholder for the vulkan backend.
When activated (`WITH_VULKAN_BACKEND=On` and `--gpu-backend vulkan`)
it might open a blender screen, but nothing should be visible as
none of the functions are implemented or otherwise crash on a nullptr.
This is expected as this is just a placeholder. The goal is to add shader compilation
+validation to this backend as one of the next steps so we can validate
changes to existing shaders on OpenGL, Metal and Vulkan at the same time.
Reviewed By: fclem
Differential Revision: https://developer.blender.org/D16338
