pgsql: Improve and cleanup ProcArrayAdd(), ProcArrayRemove().

Improve and cleanup ProcArrayAdd(), ProcArrayRemove().

941697c3c1a changed ProcArrayAdd()/Remove() substantially. As reported by
zhanyi, I missed that due to the introduction of the PGPROC->pgxactoff
ProcArrayRemove() does not need to search for the position in
procArray->pgprocnos anymore - that's pgxactoff. Remove the search loop.

The removal of the search loop reduces assertion coverage a bit - but we can
easily do better than before by adding assertions to other loops over
pgprocnos elements.

Also do a bit of cleanup, mostly by reducing line lengths by introducing local
helper variables and adding newlines.

Author: zhanyi <w(at)hidva(dot)com>
Author: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/tencent_5624AA3B116B3D1C31CA9744@qq.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/d8e950d3ae7b33a2064a4fb39b7829334b0b47bc

Modified Files
--------------
src/backend/storage/ipc/procarray.c | 133 +++++++++++++++++++++---------------
1 file changed, 78 insertions(+), 55 deletions(-)