[3.13] gh-130664: support '_' (just as ',') in Decimal's formatting (GH-132155) (#136649)

gh-130664: support '_' (just as ',') in Decimal's formatting (GH-132155)
(cherry picked from commit e10fe81cc6ae0979938eb3925139d56a74c620e3)

Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>