Move `data/shaders` to `data/shaders/glsl`
Move `data/hlsl` to `data/shaders/hlsl`
Fix up shader paths in the cpp files to point to the new glsl location.
`data/shaders/hlsl/compile.py` still overwrites the glsl .spv files (for
now).
Issue: #723
The SPIRV previously checked in had various issues -- most commonly, it
would use the VertexId and InstanceId builtins rather than the
replacmenet VertexIndex and InstanceIndex builtins required by Vulkan.
