[libc++] Implement P1165R1 (Make stateful allocator propagation more consistent)

Reviewed By: Quuxplusone, ldionne, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D119112

GitOrigin-RevId: 1cfa4857693b405d21272414442b635d9678916e