pgsql: Fix restore of not-null constraints with inheritance

Fix restore of not-null constraints with inheritance

In tables with primary keys, pg_dump creates tables with primary keys by
initially dumping them with throw-away not-null constraints (marked "no
inherit" so that they don't create problems elsewhere), to later drop
them once the primary key is restored. Because of a unrelated
consideration, on tables with children we add not-null constraints to
all columns of the primary key when it is created.

If both a table and its child have primary keys, and pg_dump happens to
emit the child table first (and its throw-away not-null) and later its
parent table, the creation of the parent's PK will fail because the
throw-away not-null constraint collides with the permanent not-null
constraint that the PK wants to add, so the dump fails to restore.

We can work around this problem by letting the primary key "take over"
the child's not-null. This requires no changes to pg_dump, just two
changes to ALTER TABLE: first, the ability to convert a no-inherit
not-null constraint into a regular inheritable one (including recursing
down to children, if there are any); second, the ability to "drop" a
constraint that is defined both directly in the table and inherited from
a parent (which simply means to mark it as no longer having a local
definition).

Secondarily, change ATPrepAddPrimaryKey() to acquire locks all the way
down the inheritance hierarchy, in case we need to recurse when
propagating constraints.

These two changes allow pg_dump to reproduce more cases involving
inheritance from versions 16 and older.

Lastly, make two changes to pg_dump: 1) do not try to drop a not-null
constraint that's marked as inherited; this allows a dump to restore
with no errors if a table with a PK inherits from another which also has
a PK; 2) avoid giving inherited constraints throwaway names, for the
rare cases where such a constraint survives after the restore.

Reported-by: Andrew Bille <andrewbille(at)gmail(dot)com>
Reported-by: Justin Pryzby <pryzby(at)telsasoft(dot)com>
Discussion: https://postgr.es/m/CAJnzarwkfRu76_yi3dqVF_WL-MpvT54zMwAxFwJceXdHB76bOA@mail.gmail.com
Discussion: https://postgr.es/m/Zh0aAH7tbZb-9HbC@pryzbyj2023

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d9f686a72ee91f6773e5d2bc52994db8d7157a8e

Modified Files
--------------
src/backend/catalog/heap.c | 36 +++++++++++++++--
src/backend/catalog/pg_constraint.c | 43 +++++++++++++-------
src/backend/commands/tablecmds.c | 65 +++++++++++++++++++++++++++----
src/bin/pg_dump/pg_dump.c | 26 +++++++++++--
src/include/catalog/pg_constraint.h | 2 +-
src/test/regress/expected/constraints.out | 56 ++++++++++++++++++++++++++
src/test/regress/sql/constraints.sql | 22 +++++++++++
7 files changed, 221 insertions(+), 29 deletions(-)