pgsql: Improve the naming of Parallel Hash Join phases.

Improve the naming of Parallel Hash Join phases.

* Commit 3048898e dropped -ING from PHJ wait event names. Update the
corresponding barrier phases names to match.

* Rename the "DONE" phases to "FREE". That's symmetrical with
"ALLOCATE", and names the activity that actually happens in that phase
(as we do for the other phases) rather than a state. The bug fixed by
commit 8d578b9b might have been more obvious with this name.

* Rename the batch/bucket growth barriers' "ALLOCATE" phases to
"REALLOCATE", a better description of what they do.

* Update the high level comments about phases to highlight phases
are executed by a single process with an asterisk (mostly memory
management phases).

No behavior change, as this is just improving internal identifiers. The
only user-visible sign of this is that a couple of wait events' display
names change from "...Allocate" to "...Reallocate" in pg_stat_activity,
to stay in sync with the internal names.

Reviewed-by: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Discussion: https://postgr.es/m/CA%2BhUKG%2BMDpwF2Eo2LAvzd%3DpOh81wUTsrwU1uAwR-v6OGBB6%2B7g%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8fba928fd78856712f69d96852f8061e77390fda

Modified Files
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doc/src/sgml/monitoring.sgml | 20 ++++----
src/backend/executor/nodeHash.c | 73 +++++++++++++-------------
src/backend/executor/nodeHashjoin.c | 90 +++++++++++++++++----------------
src/backend/utils/activity/wait_event.c | 12 ++---
src/include/executor/hashjoin.h | 38 +++++++-------
src/include/utils/wait_event.h | 4 +-
6 files changed, 119 insertions(+), 118 deletions(-)