pgsql: Extract make_SAOP_expr() function from match_orclause_to_indexco

Extract make_SAOP_expr() function from match_orclause_to_indexcol()

This commit extracts the code to generate ScalarArrayOpExpr on top of the list
of expressions from match_orclause_to_indexcol() into a separate function
make_SAOP_expr(). This function was extracted to be used in optimization for
conversion of 'x IN (VALUES ...)' to 'x = ANY ...'. make_SAOP_expr() is
placed in clauses.c file as only two additional headers were needed there
compared with other places.

Discussion: https://postgr.es/m/0184212d-1248-4f1f-a42d-f5cb1c1976d2%40tantorlabs.com
Author: Alena Rybakina <a(dot)rybakina(at)postgrespro(dot)ru>
Author: Andrei Lepikhov <lepihov(at)gmail(dot)com>
Reviewed-by: Ivan Kush <ivan(dot)kush(at)tantorlabs(dot)com>
Reviewed-by: Alexander Korotkov <aekorotkov(at)gmail(dot)com>

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d48d2e2dc8be50d3ca13305b5699384329b15433

Modified Files
--------------
src/backend/optimizer/path/indxpath.c | 62 +--------------------------
src/backend/optimizer/util/clauses.c | 81 +++++++++++++++++++++++++++++++++++
src/include/optimizer/optimizer.h | 5 +++
3 files changed, 88 insertions(+), 60 deletions(-)