Fix the deprecation warning of `stdext::checked_array_iterator`

[frederick-vs-ja]

By adding a non-deprecated copy of checked_array_iterator.

The implementation heavily relies on the implementation details of MSVC STL, but IMO this is OK since we only use it when defined(_ITERATOR_DEBUG_LEVEL) && _ITERATOR_DEBUG_LEVEL != 0.

Fixes #1768.

[robert-andrzejuk]

This should use std::span.

[lederernc]

This should use std::span.

It looks like the rest of the code base is targeting something much older than C++20.

I think this is fine as is.

[kobykahane]

@barcharcraz Can you review this?