pgsql: Fix typos and grammar in documentation and code comments

Fix typos and grammar in documentation and code comments

Comment fixes are applied on HEAD, and documentation improvements are
applied on back-branches where needed.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20210408164008.GJ6592@telsasoft.com
Backpatch-through: 9.6

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/609b0652af00374b89411ea2613fd5bb92bca92c

Modified Files
--------------
doc/src/sgml/config.sgml | 10 +++++-----
doc/src/sgml/func.sgml | 16 ++++++++--------
doc/src/sgml/logical-replication.sgml | 11 +++++------
doc/src/sgml/maintenance.sgml | 2 +-
doc/src/sgml/monitoring.sgml | 2 +-
doc/src/sgml/perform.sgml | 4 ++--
doc/src/sgml/pgstatstatements.sgml | 2 +-
doc/src/sgml/postgres-fdw.sgml | 9 +++++----
doc/src/sgml/ref/create_table.sgml | 4 ++--
doc/src/sgml/ref/createuser.sgml | 2 +-
doc/src/sgml/ref/declare.sgml | 2 +-
doc/src/sgml/ref/pg_amcheck.sgml | 2 +-
doc/src/sgml/ref/psql-ref.sgml | 7 ++++---
doc/src/sgml/wal.sgml | 2 +-
src/backend/catalog/heap.c | 1 +
src/backend/commands/analyze.c | 2 +-
src/backend/commands/cluster.c | 2 +-
src/backend/commands/copyfrom.c | 2 +-
src/backend/statistics/extended_stats.c | 2 +-
src/backend/utils/adt/jsonfuncs.c | 4 ++--
src/bin/pg_amcheck/t/004_verify_heapam.pl | 2 +-
src/include/lib/sort_template.h | 2 +-
src/include/utils/guc.h | 13 ++++++-------
23 files changed, 53 insertions(+), 52 deletions(-)