pgsql: Change the display of WAL usage statistics in Explain.

Change the display of WAL usage statistics in Explain.

In commit 33e05f89c5, we have added the option to display WAL usage
statistics in Explain and auto_explain.  The display format used two spaces
between each field which is inconsistent with Buffer usage statistics which
is using one space between each field.  Change the format to make WAL usage
statistics consistent with Buffer usage statistics.

This commit also changed the usage of "full page writes" to
"full page images" for WAL usage statistics to make it consistent with
other parts of code and docs.

Author: Julien Rouhaud, Amit Kapila
Reviewed-by: Justin Pryzby, Kyotaro Horiguchi and Amit Kapila
Discussion: https://postgr.es/m/CAB-hujrP8ZfUkvL5OYETipQwA=e3n7oqHFU=4ZLxWS_Cza3kQQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/69bfaf2e1de49de76d7dec1c45511932a5ef502b

Modified Files
--------------
.../pg_stat_statements--1.7--1.8.sql                 |  2 +-
contrib/pg_stat_statements/pg_stat_statements.c      |  6 +++---
doc/src/sgml/pgstatstatements.sgml                   |  4 ++--
doc/src/sgml/ref/explain.sgml                        |  4 ++--
src/backend/access/heap/vacuumlazy.c                 |  4 ++--
src/backend/access/transam/xlog.c                    |  4 ++--
src/backend/access/transam/xloginsert.c              | 12 ++++++------
src/backend/commands/explain.c                       | 20 ++++++++++----------
src/backend/executor/instrument.c                    |  4 ++--
src/include/access/xlog.h                            |  2 +-
src/include/executor/instrument.h                    |  2 +-
11 files changed, 32 insertions(+), 32 deletions(-)