Provide a "safe" and "simple" way for binary I/O about gsl

[dmitrykobets-msft]

Hi @jdgarciauc3m,
Thanks for submitting this issue 😃. Since the questions here are discussing interfaces that aren't fully specified by the Core Guidelines, I've forwarded the question to that repo (isocpp/CppCoreGuidelines#2067), along with some thoughts/comments.

[hsutter]

Maintainers call: The Core Guidelines maintainers prefer not to add individual span overloads/wrappers for standard library interfaces that take raw pointers and lengths, that should be in the standard. We've asked the standards committee to do this and there is interest in making span interfaces throughout the standard library including this example.