pgsql: Add \if support to pgbench

Add \if support to pgbench

Patch adds \if to pgbench as it done for psql. Implementation shares condition
stack code with psql, so, this code is moved to fe_utils directory.

Author: Fabien COELHO with minor editorization by me
Review by: Vik Fearing, Fedor Sigaev
Discussion: https://www.postgresql.org/message-id/flat/alpine(dot)DEB(dot)2(dot)20(dot)1711252200190(dot)28523(at)lancre

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f67b113ac62777d18cd20d3c4d05be964301b936

Modified Files
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doc/src/sgml/ref/pgbench.sgml | 15 +
doc/src/sgml/ref/psql-ref.sgml | 2 +-
src/bin/pgbench/pgbench.c | 359 +++++++++++++++++++----
src/bin/pgbench/t/001_pgbench_with_server.pl | 43 ++-
src/bin/pgbench/t/002_pgbench_no_server.pl | 52 ++++
src/bin/psql/Makefile | 2 +-
src/bin/psql/command.h | 2 +-
src/bin/psql/prompt.h | 2 +-
src/bin/psql/psqlscanslash.l | 2 +-
src/fe_utils/Makefile | 2 +-
src/{bin/psql => fe_utils}/conditional.c | 31 +-
src/{bin/psql => include/fe_utils}/conditional.h | 23 +-
12 files changed, 460 insertions(+), 75 deletions(-)