pgsql: Use bump memory context for tuplesorts

Use bump memory context for tuplesorts

29f6a959c added a bump allocator type for efficient compact allocations.
Here we make use of this for non-bounded tuplesorts to store tuples.
This is very space efficient when storing narrow tuples due to bump.c
not having chunk headers.  This means we can fit more tuples in work_mem
before spilling to disk, or perform an in-memory sort touching fewer
cacheline.

Author: David Rowley
Reviewed-by: Nathan Bossart
Reviewed-by: Matthias van de Meent
Reviewed-by: Tomas Vondra
Reviewed-by: John Naylor
Discussion: https://postgr.es/m/CAApHDvqGSpCU95TmM=Bp=6xjL_nLys4zdZOpfNyWBk97Xrdj2w@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6ed83d5fa55cf6e6c9d1be34ec10730c48eba763

Modified Files
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src/backend/utils/sort/tuplesort.c         | 52 +++++++++++++++++-------------
src/backend/utils/sort/tuplesortvariants.c | 38 +++++++++++++++++++---
src/include/utils/tuplesort.h              | 21 +++++++++---
3 files changed, 78 insertions(+), 33 deletions(-)