WIP: ORCA: Fix eliminate self comparison

[fanfuxiaoran]

For the below query

create table t1(a int, b int not null);
create table t2(like t1);
select t1.*, t2.* from t1 full join t2 on false where (t1.b < t1.b) is null;

orca generates a wrong plan:

Result  (cost=0.00..0.00 rows=0 width=16)
    One-Time Filter: false
Optimizer: Pivotal Optimizer (GPORCA)

The root cause is '(t1.b < t1.b)' is been transformed into 'CScalarConst (0)' by 'PexprEliminateSelfComparison'. The reason is that when checking if the selfcomparison can be simplified by function FSelfComparison, it checks the CColRef IsNullable only from the column definition, not checking if the column is from outer join.

To fix it, before simplifing the scalar expression, we fisrt get the 'pcrsNotNull' from its parent expression. 'pcrsNotNull' recoreds the output columns' nullable property. If the column is not in 'pcrsNotNull', then the self comparison cannot be transformed into const true or false.

Fixes #594

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
• [ ] Requested review from cloudberry committers

Additional Context

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