pgsql: Refactor sending of RowDescription messages in replication proto

Refactor sending of RowDescription messages in replication protocol

Some routines open-coded the construction of RowDescription messages.
Instead, we have support for doing this using tuple descriptors and
DestRemoteSimple, so use that instead.

Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/7e4fdbdc-699c-4cd0-115d-fb78a957fc22@enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2ce648f750a91b04bfa371a8f966703a382fcc97

Modified Files
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src/backend/access/common/tupdesc.c       |  9 ++++
src/backend/replication/basebackup_copy.c | 74 ++++++++++---------------------
src/backend/replication/walsender.c       | 29 ++++--------
3 files changed, 40 insertions(+), 72 deletions(-)