pgsql: Allow passing a pointer to GetNamedDSMSegment()'s init callback.

Allow passing a pointer to GetNamedDSMSegment()'s init callback.

This commit adds a new "void *arg" parameter to
GetNamedDSMSegment() that is passed to the initialization callback
function. This is useful for reusing an initialization callback
function for multiple DSM segments.

Author: Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>
Reviewed-by: Sami Imseih <samimseih(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAN4CZFMjh8TrT9ZhWgjVTzBDkYZi2a84BnZ8bM%2BfLPuq7Cirzg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/48d4a1423d2e92d10077365532d92e059ba2eb2e

Modified Files
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contrib/pg_prewarm/autoprewarm.c | 4 ++--
doc/src/sgml/xfunc.sgml | 9 ++++++---
src/backend/storage/ipc/dsm_registry.c | 8 +++++---
src/include/storage/dsm_registry.h | 4 ++--
src/test/modules/injection_points/injection_points.c | 6 +++---
src/test/modules/test_dsa/test_dsa.c | 6 +++---
src/test/modules/test_dsm_registry/test_dsm_registry.c | 7 +++++--
7 files changed, 26 insertions(+), 18 deletions(-)