legacy: move hardlink helpers, NSIndex1, AES, and PBKDF2 key file methods to borg.legacy, refs #9556#9664

ThomasWaldmann merged 5 commits into

borgbackup:masterborgbackup/borg:masterfrom

mr-raj12:legacy-phase6-cryptomr-raj12/borg:legacy-phase6-cryptoCopy head branch name to clipboard