pgsql: HashAgg: use Bump allocator for hash TupleHashTable entries.

HashAgg: use Bump allocator for hash TupleHashTable entries.

The entries aren't freed until the entire hash table is destroyed, so
use the Bump allocator to improve allocation speed, avoid wasting
space on the chunk header, and avoid wasting space due to the
power-of-two allocations.

Discussion: https://postgr.es/m/CAApHDvqv1aNB4cM36FzRwivXrEvBO_LsG_eQ3nqDXTjECaatOQ@mail.gmail.com
Reviewed-by: David Rowley

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/cc721c459d3783bbdb4beb1bbfa802a5328d15a2

Modified Files
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src/backend/executor/execUtils.c | 17 +++---
src/backend/executor/nodeAgg.c | 111 ++++++++++++++++++++++++++++++++-------
src/include/nodes/execnodes.h | 5 +-
3 files changed, 104 insertions(+), 29 deletions(-)