Add P3222R0: "Fix C++26 by adding transposed special cases for P2642 layouts"

[mhoemmen]

I've already submitted this for the 2024/04/16 mailing.

Abstract:

We propose to change the C++ Working Paper so that linalg::transposed includes special cases for layout_left_padded and layout_right_padded. These are the two mdspan layouts proposed by P2642R6, which was voted into the C++ Working Draft at the Tokyo 2024 WG21 meeting. This change will make it easier for linalg implementations to optimize for these two layouts by dispatching to an existing optimized C or Fortran BLAS. Delaying this until after C++26 would be a breaking change.

Fixes #448