pgsql: Fix race condition in XLogLogicalInfo and ProcSignal initializat

Fix race condition in XLogLogicalInfo and ProcSignal initialization.

Previously, InitializeProcessXLogLogicalInfo() was called before
ProcSignalInit(). This created a window where a process could miss a
signal barrier if it was issued between these two calls. As a result,
the process could fail to update its local XLogLogicalInfo cache,
leading to an inconsistent logical decoding state.

This commit fixes this by moving InitializeProcessXLogLogicalInfo()
after ProcSignalInit(). This ensures that the process is registered to
participate in signal barriers before its state is initialized,
preventing it from missing any state changes propagated during the
startup sequence.

Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAD21AoBzdeSyLSSPM5E6ysN1r8qzp8u_BRmnLvuAp_S8QxS_fQ@mail.gmail.com
Discussion: https://postgr.es/m/CAD21AoBj+zKvgw_Q8gjr4YbKccW_uMe3OFQ5+KT246FHUuNXSQ@mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/b384cdb2745b56121426605d985210896555fc05

Modified Files
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src/backend/postmaster/auxprocess.c | 8 ++++++++
src/backend/utils/init/postinit.c | 13 ++++++++++---
2 files changed, 18 insertions(+), 3 deletions(-)