rework VertexLayout; properly separate it from the asset loading.

include/vkcv/PipelineConfig.hpp

include/vkcv/ShaderProgram.hpp

include/vkcv/VertexLayout.hpp

modules/asset_loader/include/vkcv/asset/asset_loader.hpp

projects/cmd_sync_test/src/main.cpp

projects/first_mesh/src/main.cpp

projects/first_triangle/src/main.cpp

src/vkcv/PipelineConfig.cpp

src/vkcv/PipelineManager.cpp

src/vkcv/ShaderProgram.cpp

src/vkcv/VertexLayout.cpp