P2845R8 Formatting `filesystem::path`

[StephanTLavavej]

WG21-P2845R8 Formatting filesystem::path
WG21-P2319R5 Prevent Path Presentation Problems

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We'll also need to complete the enable_nonlocking_formatter_optimization specialization per WG21-P3235R3 "std::print More Types Faster With Less Memory".

Feature-test macro:

#define __cpp_lib_format_path 202506L

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.