refactor: re-add ATExecAlterChildConstr()
ATExecAlterChildConstr() was removed in commit
80d7f990496, but it is
needed in some subsequent patches for the NOT ENFORCED feature, to
recurse over child constraints. This adds it back in slightly altered
form.
Author: Amul Sul <amul.sul@enterprisedb.com>
Reviewed-by: Alexandra Wang <alexandra.wang.oss@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CAAJ_b962c5AcYW9KUt_R_ER5qs3fUGbe4az-SP-vuwPS-w-AGA%40mail.gmail.com