pgsql: Add pg_dump support for ALTER obj DEPENDS ON EXTENSION

Add pg_dump support for ALTER obj DEPENDS ON EXTENSION

pg_dump is oblivious to this kind of dependency, so they're lost on
dump/restores (and pg_upgrade).  Have pg_dump emit ALTER lines so that
they're preserved.  Add some pg_dump tests for the whole thing, also.

Reviewed-by: Tom Lane (offlist)
Reviewed-by: Ibrar Ahmed
Reviewed-by: Ahsan Hadi (who also reviewed commit 899a04f5ed61)
Discussion: https://postgr.es/m/20200217225333.GA30974@alvherre.pgsql

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/2b9d70159154a5ff6eb2d6f09db6f8da433328aa

Modified Files
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src/bin/pg_dump/common.c                    |   1 +
src/bin/pg_dump/pg_dump.c                   | 104 ++++++++++++++++++++++++++--
src/bin/pg_dump/pg_dump.h                   |   1 +
src/test/modules/test_pg_dump/t/001_base.pl |  46 ++++++++++++
4 files changed, 146 insertions(+), 6 deletions(-)