[ConstantFolding] Add constant folding support for nextafter/nexttoward#167324

sivakusayan wants to merge 7 commits intollvm:mainllvm/llvm-project:mainfrom

sivakusayan:fix/constant-fold-nextafter-and-nexttowardsivakusayan/llvm-project:fix/constant-fold-nextafter-and-nexttowardCopy head branch name to clipboard