Re: Allow NOT VALID foreign key constraints on partitioned tables.

When adding a new FK constraint or attaching a partitioned table, where

matching FK constraints are merged, we allow the parent constraint to be NOT

VALID while the child constraint remains VALID, which is harmless. However, the

reverse scenario -- where the parent constraint is VALID and the child is NOT

VALID -- is incorrect. To address this, when merging a NOT VALID FK constraint

from the child with a VALID parent constraint, it implicitly validates the

child constraint against its existing data and marks it as VALID. This behavior

aligns with adding a new FK constraint directly to the child table, which would

also validate the existing data.