Support for shader includes

[adriengivry]

Problem this feature should fix Some shaders are implementing the same functions instead of sharing them.

Expected solution It could be nice to have to possibility to include some "Shader function file" into our shaders. We can imagine a standard #include ... directive that can be parsed by our shader loader and replaced by the content of the file to include.

[demurzasty]

How about this: https://github.com/nothings/stb/blob/master/stb_include.h? 🙂

[adriengivry]

@demurzasty Could do the trick! I've actually started to work a bit on this, I have a branch for it: https://github.com/adriengivry/Overload/tree/feature/shader_preprocessor

Only WIP stuff, I've moved to OvRendering future-proof refactoring