P2918R2 Runtime Format Strings II

[StephanTLavavej]

WG21-P2918R2 Runtime Format Strings II

INCREASED feature-test macro:

#define __cpp_lib_format 202311L

Note: We're focused on implementing the remaining library-only features in C++23. Until that's done, we will NOT be accepting PRs for C++26 features.

[seishun]

I'm taking a stab at it in https://github.com/seishun/STL/tree/format.