pgsql: Make pg_waldump report more detail information about PREPARE TRA

Make pg_waldump report more detail information about PREPARE TRANSACTION record.

This commit changes xact_desc() so that it reports the detail information about
PREPARE TRANSACTION record, like GID (global transaction identifier),
timestamp at prepare transaction, delete-on-abort/commit relations,
XID of subtransactions, and invalidation messages. These are helpful
when diagnosing 2PC-related troubles.

Author: Fujii Masao
Reviewed-by: Michael Paquier, Andrey Lepikhov, Kyotaro Horiguchi, Julien Rouhaud, Alvaro Herrera
Discussion: https://postgr.es/m/CAHGQGwEvhASad4JJnCv=0dW2TJypZgW_Vpb-oZik2a3utCqcrA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7b8a899bdeb638f46e102d1714c079a0874e9fa0

Modified Files
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src/backend/access/rmgrdesc/standbydesc.c | 4 +
src/backend/access/rmgrdesc/xactdesc.c | 140 +++++++++++++++++++++---------
src/backend/access/transam/twophase.c | 56 +-----------
src/include/access/twophase.h | 2 -
src/include/access/xact.h | 19 ++++
5 files changed, 125 insertions(+), 96 deletions(-)