pgsql: Teach autoprewarm to use the dynamic shared memory registry.

Teach autoprewarm to use the dynamic shared memory registry.

Besides showcasing the DSM registry, this prevents pg_prewarm from
stealing from the main shared memory segment's extra buffer space
when autoprewarm_start_worker() and autoprewarm_dump_now() are used
without loading the module via shared_preload_libraries.

Suggested-by: Michael Paquier
Reviewed-by: Bharath Rupireddy
Discussion: https://postgr.es/m/20231205034647.GA2705267%40nathanxps13

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/abb0b4fc03fcf5a0ca786bd88c357bf9213aa6e1

Modified Files
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contrib/pg_prewarm/autoprewarm.c | 46 +++++++++++++---------------------------
1 file changed, 15 insertions(+), 31 deletions(-)