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
- shader: add barrier at the end of each iteration to avoid writing before the reading finished
- cpp: add synchronization between compute and graphics, the image barrier is not enough for the data visibility between different submission
modified: data/shaders/computenbody/particle_calculate.comp
modified: data/shaders/computenbody/particle_calculate.comp.spv
modified: examples/computenbody/computenbody.cpp
