pgsql: Fix description of WAL record blocks in hash_xlog.h

Fix description of WAL record blocks in hash_xlog.h

hash_xlog.h included descriptions for the blocks used in WAL records
that were was not completely consistent with how the records are
generated, with one block missing for SQUEEZE_PAGE, and inconsistent
descriptions used for block 0 in VACUUM_ONE_PAGE and MOVE_PAGE_CONTENTS.

This information was incorrect since c11453ce0aea, cross-checking the
logic for the record generation.

Author: Kirill Reshke <reshkekirill(at)gmail(dot)com>
Reviewed-by: Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
Discussion: https://postgr.es/m/CALdSSPj1j=a1d1hVA3oabRFz0hSU3KKrYtZPijw4UPUM7LY9zw@mail.gmail.com
Backpatch-through: 13

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a4e87604bcdfb6b877b16cc767b2ed15411c7342

Modified Files
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src/include/access/hash_xlog.h | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)