[Shading language support] Replace runtime GLSL shader compilation with offline compilation

[SaschaWillems]

Ultimately after implementing #1107, #1108 and #1109 runtime GLSL shader compilations should be replaced with offline compilation in the same way we do with HLSL.

So instead of compiling shaders at runtime, GLSL shaders are compiled with CMake. We should also add the compilid SPIR-V files to the project (like we do with HLSL), so people wanting to try our samples can do so without the need of having a glsl compiler installed.

That way we can simplify some code and switching between GLSL and HLSL (or other shading languages to be added) would be no more than simply changing folders.