pgsql: pg_upgrade: Use COPY for LO metadata for upgrades from < v12.

pg_upgrade: Use COPY for LO metadata for upgrades from < v12.

Before v12, pg_largeobject_metadata was defined WITH OIDS, so
unlike newer versions, the "oid" column was a hidden system column
that pg_dump's getTableAttrs() will not pick up. Thus, for commit
161a3e8b68, we did not bother trying to use COPY for
pg_largeobject_metadata for upgrades from older versions. This
commit removes that restriction by adjusting the query in
getTableAttrs() to pick up the "oid" system column and by teaching
dumpTableData_copy() to use COPY (SELECT ...) for this catalog,
since system columns cannot be used in COPY's column list.

Reviewed-by: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/aYzuAz_ITUpd9ZvH%40nathan

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b33f753612846b20ed54e296a52a6a52a6c793bc

Modified Files
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src/bin/pg_dump/pg_backup_archiver.c | 7 +---
src/bin/pg_dump/pg_dump.c | 77 ++++++++++++++++++------------------
2 files changed, 40 insertions(+), 44 deletions(-)