pgsql: Consolidate postmaster code to launch background processes

Consolidate postmaster code to launch background processes

Much of the code in process_pm_child_exit() to launch replacement
processes when one exits or when progressing to next postmaster state
was unnecessary, because the ServerLoop will launch any missing
background processes anyway. Remove the redundant code and let
ServerLoop handle it.

In ServerLoop, move the code to launch all the processes to a new
subroutine, to group it all together.

Reviewed-by: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/8f2118b9-79e3-4af7-b2c9-bd5818193ca4@iki.fi

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/3354f85284dc5439c25b57e002e62a88490aca1e

Modified Files
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src/backend/postmaster/postmaster.c | 279 ++++++++++++++++--------------------
1 file changed, 122 insertions(+), 157 deletions(-)