process startup: Do InitProcess() at the same time regardless of EXEC_BACKEND.
An upcoming patch splits single user mode into its own function. This makes
that easier. Split out for easier review / testing.
Reviewed-By: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Author: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/
20210802164124.ufo5buo4apl6yuvs@alap3.anarazel.de