hs: Move cell encoding/decoding out of hs_intropoint.c to hs_cell.c
The hs_cell.c
file is added by #20657 (moved) so once it's merged, let's do this so we don't have cell mangling in different files everywhere.
The hs_cell.c
file is added by #20657 (moved) so once it's merged, let's do this so we don't have cell mangling in different files everywhere.