pgsql: Injection points for hash aggregation.

Injection points for hash aggregation.

Requires adding a guard against shift-by-32. Previously, that was
impossible because the number of partitions was always greater than 1,
but a new injection point can force the number of partitions to 1.

Discussion: https://postgr.es/m/ff4e59305e5d689e03cd256a736348d3e7958f8f.camel@j-davis.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/38172d1856b34792a5ee60eaa0d883166e90d33d

Modified Files
--------------
src/backend/executor/nodeAgg.c | 48 ++++++++++++++-
src/test/modules/injection_points/Makefile | 2 +-
.../modules/injection_points/expected/hashagg.out | 68 ++++++++++++++++++++++
src/test/modules/injection_points/meson.build | 1 +
src/test/modules/injection_points/sql/hashagg.sql | 26 +++++++++
5 files changed, 141 insertions(+), 4 deletions(-)