pgsql: doc: Correct psql's \d+x documentation for sequences

doc: Correct psql's \d+x documentation for sequences

Commit 00f4c2959d6 added the x modifier to psql's list commands, making
\d+x display sequence descriptions in expanded mode. However, the
documentation and \? help indicate that x applies only without a pattern.

Clarify that \d+x also uses expanded mode when describing sequences
matched by a name or pattern, and update the command help accordingly.
Also clarify that the same restriction applies to \x on and \x auto.

Backpatch to v18, where the x modifier was introduced.

Reported-by: George MacKerron <george(dot)mackerron(at)databricks(dot)com>
Author: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Reviewed-by: Shihao Zhong <zhong950419(at)gmail(dot)com>
Discussion: https://postgr.es/m/FEA91EA9-CF32-4920-9674-F2C3E01C3807@databricks.com
Backpatch-through: 18

Branch
------
REL_18_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/4272618fbb83f1522e68626f70f0dee4628b73f2

Modified Files
--------------
doc/src/sgml/ref/psql-ref.sgml | 11 +++++++----
src/bin/psql/help.c | 3 ++-
2 files changed, 9 insertions(+), 5 deletions(-)