During the ISO C++ Committee meeting plenary session the C++23 Standard
has been voted as technical complete.
This updates the reference to c++2b to c++23 and updates the __cplusplus
macro.
Drive-by fixes c++1z -> c++17 and c++2a -> c++20 when seen.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D149553
After accepted in Kona, update the code to accept static operator[] as well.
No big code changes: accept this operator as static in SemaDeclCXX, update AST call generation in SemaOverload and update feature macros + tests accordingly.
Reviewed By: cor3ntin, erichkeane, #clang-language-wg
Differential Revision: https://reviews.llvm.org/D138387