P2944R3: Constrained equality - set FTM `__cpp_lib_constrained_equality`

[Zingam]

202403L for P2944R3
202411L for P3379R0

[H-G-Hristov]

__cpp_lib_constrained_equality

• 202403L for P2944R3 - [libc++] Implement comparison operators for tuple added in C++23 #148799
• 202411L for P3379R0 - [libc++] Implement P3379R0 Constrain std::expected equality operators #135759