Make pg_dump emit ATTACH PARTITION instead of PARTITION OF (reprise)

Using PARTITION OF can result in column ordering being changed from the
database being dumped, if the partition uses a column layout different
from the parent's.  It's not pg_dump's job to editorialize on table
definitions, so this is not acceptable; back-patch all the way back to
pg10, where partitioned tables where introduced.

This change also ensures that partitions end up in the correct
tablespace, if different from the parent's; this is an oversight in
ca410302 (in pg12 only).  Partitioned indexes (in pg11) don't have
this problem, because they're already created as independent indexes and
attached to their parents afterwards.

This change also has the advantage that the partition is restorable from
the dump (as a standalone table) even if its parent table isn't
restored.

The original commits (3b23552a in branch master) failed to cover
subsidiary column elements correctly, such as NOT NULL constraint and
CHECK constraints, as reported by Rushabh Lathia (initially as a failure
to restore serial columns).  They were reverted.  This recapitulation
commit fixes those problems.

Add some pg_dump tests to verify these things more exhaustively,
including constraints with legacy-inheritance tables, which were not
tested originally.  In branches 10 and 11, add a local constraint to the
pg_dump test partition that was added by commit 2d7eeb1b to master.

Author: Álvaro Herrera, David Rowley
Reviewed-by: Álvaro Herrera
Discussion: https://postgr.es/m/CAKJS1f_1c260nOt_vBJ067AZ3JXptXVRohDVMLEBmudX1YEx-A@mail.gmail.com
Discussion: https://postgr.es/m/20190423185007.GA27954@alvherre.pgsql
Discussion: https://postgr.es/m/CAGPqQf0iQV=PPOv2Btog9J9AwOQp6HmuVd6SbGTR_v3Zp2XT1w@mail.gmail.com