[#76] WIP: use vk::ShaderStageFlagBits to allow descriptors to use multiple shader stages.

config/Sources.cmake

include/vkcv/Core.hpp

include/vkcv/DescriptorConfig.hpp

include/vkcv/ShaderProgram.hpp

include/vkcv/ShaderStage.hpp

modules/material/include/vkcv/material/PBRMaterial.hpp

modules/material/src/vkcv/material/PBRMaterial.cpp

modules/shader_compiler/include/vkcv/shader/Compiler.hpp

modules/shader_compiler/include/vkcv/shader/GLSLCompiler.hpp

modules/shader_compiler/src/vkcv/shader/GLSLCompiler.cpp

projects/bloom/src/BloomAndFlares.cpp

projects/bloom/src/main.cpp

projects/first_mesh/src/main.cpp

projects/first_scene/src/main.cpp

projects/first_triangle/src/main.cpp

projects/particle_simulation/src/BloomAndFlares.cpp

projects/particle_simulation/src/main.cpp

projects/voxelization/src/BloomAndFlares.cpp

projects/voxelization/src/ShadowMapping.cpp

projects/voxelization/src/Voxelization.cpp