Fix the build; make layout_transpose and conjugated_accessor conform

[mhoemmen]

This fixes the build, which is currently broken, thus blocking any new features.

1. Change this repository so that it no longer uses or depends on std::experimental.

2. Fix layout_transpose to conform with the Standard. It had implemented an older version of mdspan that used size_type instead of index_type.

3. Rename accessor_conjugate to conjugated_accessor and otherwise bring it in line with the Standard. Improve tests for conjugated.

This is rebased atop https://github.com/kokkos/stdBLAS/pull/264 which I submitted in January but hasn't yet been merged. Please either merge that one first, or close that one and merge this one.

[mhoemmen]

@dalg24 wrote:

I scrolled through the changes of the last 3 commits (that is excluding the changes from the PR that I just merged) and it looks good besides https://github.com/kokkos/stdBLAS/pull/269/files/2584d02d3230805525db529d39033982c3120fc2..ca3f2614dfa5d6edb2abb7bdcbc508d90a56eeef#r1550159723 If you withdraw these addition I will approve and merge

Fixing the merge conflicts seems to have made this link invalid. My understanding is that you were referring to the new tests in tests/native/transposed.cpp. Those tests only exercise current P1673R13 features. As I explained above,

• transposed of layout_left is layout_right,
• transposed of layout_right is layout_left, and
• transposed of layout_stride is layout_stride.

That has always been true; this has nothing to do with any new proposals.