pgsql: psql: Rename meta-command \close to \close_prepared

psql: Rename meta-command \close to \close_prepared

\close has been introduced in d55322b0da60 to be able to close a
prepared statement using the extended protocol in psql.  Per discussion,
the name "close" is ambiguous.  At the SQL level, CLOSE is used to close
a cursor.  At protocol level, the close message can be used to either
close a statement or a portal.

This patch renames \close to \close_prepared to avoid any ambiguity and
make it clear that this is used to close a prepared statement.  This new
name has been chosen based on the feedback from the author and the
reviewers.

Author: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: https://postgr.es/m/3e694442-0df5-4f92-a08f-c5d4c4346b85@eisentraut.org

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/fc39b286ad7262a4aac8ff9a34f244763bed7a53

Modified Files
--------------
doc/src/sgml/ref/psql-ref.sgml              |  8 ++++----
doc/src/sgml/release-18.sgml                |  2 +-
src/bin/psql/command.c                      | 12 ++++++------
src/bin/psql/common.c                       |  2 +-
src/bin/psql/help.c                         |  3 ++-
src/bin/psql/tab-complete.in.c              |  2 +-
src/test/regress/expected/psql.out          | 14 +++++++-------
src/test/regress/expected/psql_pipeline.out |  6 +++---
src/test/regress/sql/psql.sql               | 12 ++++++------
src/test/regress/sql/psql_pipeline.sql      |  6 +++---
10 files changed, 34 insertions(+), 33 deletions(-)