AMReX C++20 in VS2026

[ax3l]

According to a non-descript bug report in WarpX, AMReX might not yet compile with the latest VS 2026 (MSVC) for Windows. VS 2026 uses C++20 by default, so I suspect it is somehow related to C++20 in MSVC.

We should update our CI runners to add a C++20 build in those and fix issues that we see.