[libc++] Implement P1272R4 (std::byteswap)

Implement P1274R4

Reviewed By: Quuxplusone, Mordante, #libc

Spies: jloser, lebedev.ri, mgorny, libcxx-commits, arichardson

Differential Revision: https://reviews.llvm.org/D114074

GitOrigin-RevId: 1dc62f2653f837745251bd905940c11962469b45
12 files changed