[YSQL] Support expression pushdown for DOMAIN types

[timothy-e]

Jira Link: DB-15652

Description

CREATE DOMAIN posint AS integer CHECK (VALUE > 0);
CREATE TABLE test_domain_tbl (d_col posint, i_col int);
INSERT INTO test_domain_tbl VALUES(1, 2);
EXPLAIN (COSTS OFF) SELECT * FROM test_domain_tbl WHERE d_col > 1 AND i_col > 1;
            QUERY PLAN
----------------------------------
 Seq Scan on test_domain_tbl
   Storage Filter: (i_col > 1)
   Filter: ((d_col)::integer > 1)
(3 rows)

It is reasonable for the expression pushdown code to look at the type contained by the domain, and if that is a pushable type, push the expression.

Issue Type

kind/enhancement

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