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.parragi@percona.com>
Reviewed-by: Sami Imseih <samimseih@gmail.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(-)