https://timsong-cpp.github.io/cppwp/mdspan.layout.stride.obs
[mdspan.layout.stride.obs]
mdspanlayoutstrideobs
https://timsong-cpp.github.io/cppwp/n4950/mdspan.extents
[mdspan.extents]
mdspan
https://timsong-cpp.github.io/cppwp/n4950/mdspan.layout
[mdspan.layout]
mdspanlayout