pgsql: Expose wal_fpi_bytes in EXPLAIN (WAL)

Expose wal_fpi_bytes in EXPLAIN (WAL)

The new wal_fpi_bytes counter calculates the total amount of full page
images inserted in WAL records, in bytes. This commit exposes this
information in EXPLAIN (ANALYZE, WAL) alongside the existing counters,
for both the text and JSON/YAML outputs, building upon f9a09aa29520.

Author: Shinya Kato <shinya11(dot)kato(at)gmail(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discusssion: https://postgr.es/m/CAOzEurQtZEAfg6P0kU3Wa-f9BWQOi0RzJEMPN56wNTOmJLmfaQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5ab0b6a248076bf373a80bc7e83a5dfa4edf13aa

Modified Files
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doc/src/sgml/ref/explain.sgml | 3 ++-
src/backend/commands/explain.c | 8 +++++++-
2 files changed, 9 insertions(+), 2 deletions(-)