ORCA: don't push LOJ ON-pred onto its own outer in PushThruOuterChild

[yjhjstz]

Summary

Fix a wrong-result bug in ORCA where a LEFT JOIN's own ON predicate ends up duplicated as a scan filter on the join's outer relation, discarding outer rows
that LOJ semantics require to be null-padded.

Repro

CREATE TABLE x(c1 boolean);
CREATE TABLE y1(c1 boolean);
CREATE TABLE y2(c1 boolean);
INSERT INTO x  VALUES (true),(false),(false);
INSERT INTO y1 VALUES (true);
INSERT INTO y2 VALUES (true);

SET optimizer = on;
SELECT x.c1, y2.c1 AS y2c1
  FROM x LEFT JOIN y1 ON x.c1
         LEFT JOIN y2 ON x.c1
 WHERE y2.c1 IS NULL;

Optimizer	Result	Seq Scan on x
Postgres planner	2 rows (correct)	no scan filter
ORCA (before fix)	0 rows ❌	Filter: c1 ❌

Trigger: two or more chained LEFT JOINs whose ON-clauses use the same boolean column from the outer relation, with a WHERE on top.

Root cause

CNormalizer::PushThruOuterChild is invoked from PushThruSelect with a predicate that happens to be (or contain) the LOJ's own ON predicate.
SplitConjunct / FPushable accept it as pushable to the outer relation, because FPushable only checks that the predicate's columns are a subset of the
outer's output columns — an LOJ ON-pred that references only outer-side columns trivially satisfies that.

Consequence: ORCA wraps the outer with Select(outer, on_pred), producing LOJ(Select(x, c1), inner, x.c1). The LOJ's ON-pred is preserved as Join Filter, but a redundant Filter: c1 is also planted on the outer scan, which discards outer rows that don't satisfy the ON-pred — exactly the rows LOJ
must null-pad and keep.

Fixes #ISSUE_Number

What does this PR do?

Type of Change

• Bug fix (non-breaking change)
• New feature (non-breaking change)
• Breaking change (fix or feature with breaking changes)
• Documentation update

Breaking Changes

Test Plan

• Unit tests added/updated
• Integration tests added/updated
• Passed make installcheck
• Passed make -C src/test installcheck-cbdb-parallel

Impact

Performance:

User-facing changes:

Dependencies:

Checklist

• Followed contribution guide
• Added/updated documentation
• Reviewed code for security implications
• This PR contains AI-assisted code generation
• Requested review from cloudberry committers

Additional Context

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