pgsql: psql: Add more meta-commands able to use the extended protocol

psql: Add more meta-commands able to use the extended protocol

Currently, only unnamed prepared statement are supported by psql with
the meta-command \bind.  With only this command, it is not possible to
test named statement creation, execution or close through the extended
protocol.

This commit introduces three additional commands:
* \parse creates a prepared statement using the extended protocol,
acting as a wrapper of libpq's PQsendPrepare().
* \bind_named binds and executes an existing prepared statement using
the extended protocol, for PQsendQueryPrepared().
* \close closes an existing prepared statement using the extended
protocol, for PQsendClosePrepared().

This is going to be useful to add regression tests for the extended
query protocol, and I have some plans for that on separate threads.
Note that \bind relies on PQsendQueryParams().

The code of psql is refactored so as bind_flag is replaced by an enum in
_psqlSettings that tracks the type of libpq routine to execute, based on
the meta-command involved, with the default being PQsendQuery().  This
refactoring piece has been written by me, while Anthonin has implemented
the rest.

Author: Anthonin Bonnefoy, Michael Paquier
Reviewed-by: Aleksander Alekseev, Jelte Fennema-Nio
Discussion: https://postgr.es/m/CAO6_XqpSq0Q0kQcVLCbtagY94V2GxNP3zCnR6WnOM8WqXPK4nw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d55322b0da60a8798ffdb8b78ef90db0fb5be18e

Modified Files
--------------
doc/src/sgml/ref/psql-ref.sgml     |  90 +++++++++++++++++++++++++
src/bin/psql/command.c             | 130 ++++++++++++++++++++++++++++++++++++-
src/bin/psql/common.c              |  59 +++++++++++++----
src/bin/psql/help.c                |   4 ++
src/bin/psql/settings.h            |  15 ++++-
src/bin/psql/tab-complete.c        |   6 +-
src/test/regress/expected/psql.out |  55 ++++++++++++++++
src/test/regress/sql/psql.sql      |  28 +++++++-
src/tools/pgindent/typedefs.list   |   1 +
9 files changed, 369 insertions(+), 19 deletions(-)