pgsql: Add some regression tests that exercise hash join code.

Add some regression tests that exercise hash join code.

Although hash joins are already tested by many queries, these tests
systematically cover the four different states we can reach as part of
the strategy for respecting work_mem.

Author: Thomas Munro
Reviewed-By: Andres Freund

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/fa330f9adf4e83c0707b0b1164e7bf09c9204b3d

Modified Files
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src/test/regress/expected/join.out | 457 +++++++++++++++++++++++++++++++++++++
src/test/regress/sql/join.sql      | 253 ++++++++++++++++++++
2 files changed, 710 insertions(+)