pgsql: Update the names of Parallel Hash Join phases.

Update the names of Parallel Hash Join phases.

Commit 3048898e dropped -ING from some wait event names that correspond
to barrier phases. Update the phases' names to match.

While we're here making cosmetic changes, also rename "DONE" to "FREE".
That pairs better with "ALLOCATE", and describes the activity that
actually happens in that phase (as we do for the other phases) rather
than describing a state. The distinction is clearer after bugfix commit
3b8981b6 split the phase into two. As for the growth barriers, rename
their "ALLOCATE" phase to "REALLOCATE", which is probably a better
description of what happens then. Also improve the comments about
the phases a bit.

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/378802e3713c6c0fce31d2390c134cd5d7c30157

Modified Files
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src/backend/executor/nodeHash.c | 72 ++++++++++++++++----------------
src/backend/executor/nodeHashjoin.c | 83 +++++++++++++++++++------------------
src/backend/postmaster/pgstat.c | 8 ++--
src/include/executor/hashjoin.h | 38 ++++++++---------
src/include/pgstat.h | 4 +-
5 files changed, 104 insertions(+), 101 deletions(-)