[FEA] update to official padded layouts and test submdspan functionality

[mfoerste4]

This is a followup for PR #725 based on issue #497 introduced padded layouts for aligned data access layout_{left,right}_padded.

The underlying base implementation does not yet exist as header template within the reference mdspan implementation, but had to be manually created based on examples within https://github.com/kokkos/mdspan. These manual headers have been added as aligned_accessor.hpp and layout_padded.hpp.

Currently, these custom layouts are not supported by submdspan.

I suggest to update the header classes to the official ones once available and add submdspan testcases accordingly.