pgsql: Rethink pg_dump's handling of object ACLs.

Rethink pg_dump's handling of object ACLs.

Throw away most of the existing logic for this, as it was very
inefficient thanks to expensive sub-selects executed to collect
ACL data that we very possibly would have no interest in dumping.
Reduce the ACL handling in the initial per-object-type queries
to be just collection of the catalog ACL fields, as it was
originally. Fetch pg_init_privs data separately in a single
scan of that catalog, and do the merging calculations on the
client side. Remove the separate code path used for pre-9.6
source servers; there is no good reason to treat them differently
from newer servers that happen to have empty pg_init_privs.

Discussion: https://postgr.es/m/2273648.1634764485@sss.pgh.pa.us
Discussion: https://postgr.es/m/7d7eb6128f40401d81b3b7a898b6b4de@W2012-02.nidsa.loc

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/0c9d84427f441602425b0e18be5cfe751d1d8ebe

Modified Files
--------------
src/bin/pg_dump/dumputils.c | 516 ++++++---------
src/bin/pg_dump/dumputils.h | 14 +-
src/bin/pg_dump/pg_dump.c | 1199 ++++++++++++++---------------------
src/bin/pg_dump/pg_dump.h | 69 +-
src/bin/pg_dump/pg_dumpall.c | 59 +-
src/fe_utils/string_utils.c | 63 ++
src/include/fe_utils/string_utils.h | 1 +
7 files changed, 784 insertions(+), 1137 deletions(-)