pgsql: Fix tuplesort memory accounting for datum sorts on byref types

Fix tuplesort memory accounting for datum sorts on byref types

6ed83d5fa made it so tuplesorts could use a bump.c memory allocator for
non-bounded sorts in order to save memory and increase performance.
That commit didn't get the memory accounting correct for datum sorts and
mistakenly passed 0 bytes to tuplesort_puttuple_common(). That was
correct for byval types, but failed to take into account palloc'd memory
for byref types.

Fix by using datumGetSize() when using the bump allocator and by using
GetMemoryChunkSpace() when not.

Backpatch to v17, where 6ed83d5fa was added.

Author: Mario Karuza <mkaruza(dot)pg(at)icloud(dot)com>
Reviewed-by: David Rowley <dgrowleyml(at)gmail(dot)com>
Reviewed-by: Joao Detomini <joao(dot)detomini(at)enterprisedb(dot)com>
Discussion: https://postgr.es/m/e9f9f54337cd86a982837763958518cdbf08863c.camel%40icloud.com
Backpatch-through: 17

Branch
------
REL_17_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/2414028ab64bcffccfee75790a15b5960de8d095

Modified Files
--------------
src/backend/utils/sort/tuplesortvariants.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)